How do I create a formula for calculating multiple invoice type items

I cannot figure the formula that will allow me to sell products without the length and width in the line. I need to sell bulk products without dimensional sizes.

I do not want zeros to show on the invoice unless inputted.

This is the formual in the total column:

=IF(SUM(V8)>0,SUM((R8*T8)*V8)-Z8,"")


Please Help