Subtract inventory based on date

Hello,
I am trying to see if there is a way to keep an automatic total of how much inventory I have on the floor based on date.
My first column has the total I started with at the beginning of the week, and then a column for each day with the quantity sold each day. I want a new column that shows how much is currently on the floor based on what day it is. I'm currently manually adding columns to the formula each day,but obviously this is not efficient.
For example,
I start with 100 cases of product at the beginning of the week. I plan to sell 20 cases on 8/1, 10 cases on 8/2, 10 cases on 8/3, 20 cases on 8/4, and 10 cases on 8/5. How can it auto-calculate so when I open the worksheet on 8/1, it shows I have 80 cases left, and then on 8/4 the same cell shows I have 40 cases left?

Thanks in advance!

Hello and thanks for your reply. I have attached a sample version, and the highlighted area is where I'd like the current available inventory. That way, we can see how much we started with, how much we have today, and how much we'll have at the end of the week.

I have put in the expected if I opened the worksheet on 8/1. Thanks!

Thanks! I have tried it on an older week to see if it subtracts everything, and it still returns as if nothing has gone out yet. I have changed the cell formats for the headers to date, and the cells to general. What am I doing wrong?

Sorry, that was foolish wording as I try to brainstorm. I've attached the exact layout we use.

Thank you so much!!! Adding the dates above the table worked perfectly.