An office manager is buying used filing cabinets. Small file cabinets cost $5 each and large
file cabinets cost $9 each, and the manager cannot spend more than $81 on file cabinets. A
small cabinet takes up 5 square feet of floor space and a large cabinet takes up 8 square
feet, and the office has no more than 77 square feet of floor space available for file cabinets.
The manager must buy at least 5 file cabinets in order to get free delivery. Let x = the
number of small file cabinets bought and y = the number of large file cabinets bought.