formulate the sliding scale

I am trying to make a Excel Spreedsheet that i can use to quote my clients with

I need the spreadsheet to calculate the expense of the
Labour_Type_1 - Charged 1 per item type, regardless or quantity
Labour_Type_2 - Charged 1 per item type, regardless or quantity
Labour_Type_3 - Charged by quantity of each item type

Labour needs to be calculated on a sliding scale. The large the item the less I need to charge for labour.
To work out the size of the item its in mm,


Here is the formula

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The formula is checking how many can fit onto 1 sheet

$D8 is the length of the graphic designs,
$E8 is the Width of the graphic design.
C8 is the Quantity of the order.
Labour_Per_Min = Dollar Per Hour / 60
Rounding = 2
B8 = Type of Product being purchased
Expenses_Per_Order = Total Expenses and materials to complete order.
Sale_markup = the profit formula that is still to be worked out

My full formula is looking like this

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I hope this is enough information

Can anyone give me some insite to this.

I need to workout how to formulate the sliding scale for labour and get my formula to work.

I really appreciate your time

Thank you

Is there a simple formula to make using a formulated sliding scale

Variable being the Area of the design

Im thinking of something like

Percentage of Print area is the %centage of slide per item

EG
1 sheet = 1000mm Long, 580mm Wide
Area 1 = 580 000 mm2

Image size is 580mm x 100mm
Area 2 = 58 000 mm2

Area 2 / Area 1 *100 = 10%

What are your thoughts on this.

I need to make it backwards tho.

The larger the image the less labour that needs to be charged