The full price would be $25; you have $15 + $10. Now, buying reduced, it's going to be $15 + 1/2 of the $10, so she's going to be paying a total of $20. The difference between $25 and $20 is $5, and we need to find what percent $5 is of $25. 25 goes into 5 .2 times, so it's B, a 20% reduction.