I need help creating a schedule of how discounts affect my gross margin.

Starting in column A7, I have listed my discounts starting from 1 to 50. If
F3 = 100, F4= 40 & F5= 60. F4 is my cost of goods at 40%, F5 is gross margin
at 60%.

In B7, I want show the gross margin if F3 or the selling price is reduced by
1 (the discount). The calculation should be .595 as the gross margin if the
selling price is reduced by 1%.

How would I prepare the formula in b7 to calculate this?

Thanks, victor