Set up an equation when x is the cost of a book. If we know that 45 + 5 = 50: 45x = 50(x - .1) Now, multiply across the parentheses: 45x = 50x - 5 (Now, combine terms over the equal sign) -50x -50x -5x = -5 (Now, divide off the -5 from both sides) /-5 /-5 x = 1 This means that the current cost of a book is <em><u>$1.</u></em> This works out if you test it. Hope this helps! ~<em>ArchimedesEleven</em>