13. 47.50 dollars / 5 = 9.50 dollars per shirt, $9.50.
14. 39.00 dollars / 6 binders = 6.5 dollars per binder, $6.50.
15. 4.50 dollars / 2 = 2.25 dollars per spiral notebook, $2.25.
16. 180 dollars / 15 = 12 dollars per hour of work, $12.00.
17. $2.25 per spiral notebook * 7 notebooks = $15.75.
18. $6.50 per binder * 2 binders = $13.00
19. $6.50 - $2.25 = $4.25.
20. $6.50 + $9.50 + $2.25 = $18.25.