Mandy has bought some books and pens. If she buys 6 books and 5 pens, she will have $7.10 left. If she buys 4 books and 11 pens, she will need $20.10 more. If a book costs $5.90, how much money does had she have?
If she has $x, then
x - (6*5.90 + 5p) = 7.10
x = 4*5.90 + 11p - 20.10
now solve for x