The store sale 85% off only today. Ella planned to buy these skates anyway, and so she bought them immediately. If she paid $18.00. How much money did she save?

Let x be the original price. Then the discounted price is
                                         discount = x(1 - 0.85)
The discounted price is $18.00. Therefore
                                         18.00 = x(0.15)
                                                 x = 18.00 / 0.15
                                                 x = $120.00
The amount she saved is $120.00 - $18.00 = $102.00

The answer to this question is that Ella saved $102.00.