You know that the graph of the absolute-value function is a V (either right side up or upside down). The vertex (point in the V) is given by (h, k), and this represents, in our case, the optimal fuel efficiency. So h = 50 and k = 24. We're given that when r = 60 mph, m = 20 mph, so plug in:

Solve for a:

So our complete equation is

.

01