Marcia buys a dress that is on sale for 15% off it's original price. She uses a store coupon to obtain an additional 10% off the sale price. Marcia pays $91.80 for the dress. What was the original price of the dress?

15% off the original price
10% off the sale price
Sale price $91.80 

First we have to find out the price before 10% discount. 
(sale price) divided by (1 - percent of sale price)

91.80/(1 -.10) = $102

So, $102 was the price before the 10% discount. Now we need to do the same with the 15% off so that we can get the original price.

102/(1 - .15) = $120 

The original price was $120