The starting prices for both of the books are at 100%, and taking 25% from the second book it would be 75%. You will have 75% of each value of the books while they're on sale, which you can convert to decimal .75. Multiply this decimal by each of the books' values to figure out how much they'll be on sale and then add them, which would total up to 36 + 18= 54$. By dividing this value by the book's original value, 60$, would equal it to .9. Converting the .9 to a percent and subtracting it by 100%, It's reduced by 10%.
