The graph shows the amounts customers pay for x pounds of cheese at a deli counter. Customers pay a certain price per pound up to exactly 5 pounds. If a customer buys more than 5 pounds, then the price per pound for the entire purchase is discounted.

There is a cost-amount graph. Amount (lb) is plotted on the X-axis. Cost ($) is plotted on Y-axis. The X-coordinate marks 0, 4, and 8. The Y-coordinate mark 0, 10, 20, 30, and 40. There is one line segment which starts from closed point at (0, 0) and ends at closed point (5, 25). There is an arrow which starts from open point (5, 20) and increases uniformly. It passes through the point (9, 40).

Complete the following by entering a number or expression in each box.

A piecewise-defined function for the graph is

f(x) = , 0 < x ≤

, x >

Customers who buy up to 5 pounds pay $ per pound.

Customers who buy more than 5 pounds pay $20 for the first 5 pounds. They pay $ per pound for each pound over 5 pounds.