SOLUTION
Write out the given parameters
Paperback Books $5
Hardcover Books $9
Magazines $2

Hence
1) The cost of 4 hardcover books is $36
To show the result on a number line we have the diagram below
2). 3 hardcover will costs

3 paperback books will cost

If Chico bought 3 hardcover rather than 3 paperback books
chico will spend

Hence, Chico will spend $12 more