At most, Alana can spend $40 on carnival tickets. Ride tickets cost $4 each, and food tickets cost $2 each. Alana buys at least 16 tickets. The system of inequalities represents the number of ride tickets, r, and the number of food tickets, f, she buys.

r + f ≥ 16

4r + 2f ≤ 40

A graph shows r on the x-axis, from 0 to 18, and f on the y-axis, from 0 to 20. Two solid lines are shown. The first line has a negative slope and goes through (0, 20) and (10, 0). Everything to the left of the line is shaded. The second line has a negative slope and goes through (0, 16) and (16, 0). Everything above the line is shaded.
What is the maximum number of ride tickets she can buy?

4
6
10
12