First off, to find out the new discounted price without the sales tax, you multiply $24.50 by 15% (0.15). This gives you $3.68. You then subtract the $3.68 from $24.50. You get $20.82. To find the total with sales tax you then multiply the $20.82 by 10% (0.1). You add the discounted price with the sales tax and get the conclusion that they have enough money for the book.
