Automatically inserting data into multiple cells from one spreadsheet after entering a no.

[MartinMuster]

Hi everybody.
I've asked some questions here already and it helped me greatly, problem is that I've made an error of reasoning.
Let me start from the beginning.
I have an excel file which should contain all the items which are coming in and which are going out. I asked for a formula to help me keep track of the inventory and that it adds and subtracts whenever I enter someting in the 'outgoing' or 'incoming' spreadsheet. Thing is that I have different quantities when I get something and when I give something away.
Here's an example.
I get 3 packages with the item number 118, this means I have in total 300 clear folders(100 in each package) and now I give somebody 20 clear folders, when I enter 20 items with the item number 118 in 'outgoing' it deducts 20 packages from the inventory...
I don't know how I can solve this. Suggestions even if they are on a basic level would be appreciated.(Adding a spreadsheet, adding a column etc.)
It's this formula

=10+SUMIFS(Incoming!B:B,Incoming!C:C,'Writing utensils'!A2)-SUMIFS(Outgoing!B:B,Outgoing!C:C,'Writing utensils'!A2)

Another problem that I have is that I would like a formula which automatically fills in the blank cells in 'incoming' and 'outgoing' whenever I enter an item number.
I've highlighted 2 examples, one in each spreadsheet, showing you what I want to appear in those spreadsheets(yellow rows).

What's also important to keep in mind is that I have already a bunch of other formulas in place and I would appreciate if nothing stops working (except for the aforementioned formula)

=10+SUMIFS(Incoming!B:B,Incoming!C:C,'Writing utensils'!A2)-SUMIFS(Outgoing!B:B,Outgoing!C:C,'Writing utensils'!A2)
it's in the column 'Stock'within the spreadsheets 'Folder' to 'Misc.'

[FlameRetired]

The formulas in column J of the folder sheet are not all preceded by 10. They are preceded by many different numbers. Is that what you intended?

This is a sample I cropped and copied to a new workbook. Sample starts @ row 11 column J.

	A	B	C	D
1
2		=11+SUMIFS(Inco…>>
3		=8+SUMIFS(Incom…>>
4		=4+SUMIFS(Incom…>>
5		=1+SUMIFS(Incom…>>
6		=6+SUMIFS(Incom…>>
7		=6+SUMIFS(Incom…>>
8		=10+SUMIFS(Inco…>>
9		=7+SUMIFS(Incom…>>
10		=6+SUMIFS(Incom…>>
11		=10+SUMIFS(Inco…>>
12

[MartinMuster]

Thanks for you effort, but this is not what I needed. I already adjusted the formula depending on the item and how many it has of it in the inventory.
You can see in the file that I uploaded that these formulas are already just like you suggested.

[MartinMuster]

I've tried to simplify my excel file to articulate my problem better.
I have a pack of 100 clear folders. I order a pack of it and enter 1 (pack) into incoming, BUT I give out let's say 20 clear folders and not 20 packs. Problem is that I don't know how to circumvent this problem. Another spreadsheet would probably help, but I don't know how to properly do this.

[MartinMuster]

Is there a way that a formula calculates the percentage of a value after entering it and that it does it only with certain values?
Still going with 'stock_inventory 2.xlsx' from the previous post.
Let's say that when I enter in 'Incoming' Item number 6 and quantity 1. Is it possible that it checks how big a pack is and THEN adds 1 to the stock?
The other thing would be I enter in 'Outgoing' item number 1 and quantity 10. Is it possible that it checks how big a pack is and if it is bigger than 1 it calculates the percentage of the added or substracted value and adds it(detracts it) from the stock in 'Folder'?

[MartinMuster]

I found a solution to my problem. Instead of trying to calculate how much of a package gets deducted, I just have to say that every item's 'Pack' has only 1 unit and divide the cost of each pack with the actual amount that I'm ordering.

SOLVED.