Question

Jamie has saved $42 of her allowance money to buy books. If she buys 5 books at d dollars per book, she will have 42-5d of her allowance left. How much does she have left if the books cost $3.50 each?

Answer 1

1.42-5(3.50)
2.42-17.50
3.$24.50 left

Answer 2

If d in the equation is the cost of each book and each book is $3.50 the equation will look like this 
42 - 5($3.50) 

42 - 17.50 

24.50

Once the equation is solved your left with the answer which is $24.50 

Hope this helps! :)