Question

What is the original price if there is a 10% discount and the sale price is 76.50?

Answer 1

Let the original price = x
then  76.50 = 0.90x
x = 76.50 / 0.90 = 85 

Answer 2

This being algebra, your best bet would be to represent the "original price" by a letter, such as n.

If there's a 10% discount on this item, the price you'd pay would be (1-0.10)n, and this price is $76.50

Solve (1-0.10)n = $76.50 for n.