Let x = original price in dollars
x is the original price
9% of this original price is equal to 0.09x
subtract: x - 0.09x = 0.91x
The discount price is equal to 0.91x and it's equal to 90 dollars, so they must be the same value. Ie.
0.91x = 90
0.91x/0.91 = 90/0.91
x = 98.9010989
x = 98.90
So the original price is $98.90
