A pay-as-you-go cell phone company offers a monthly plan for $19 that includes 200 minutes of calls. After that, calls are an additional 4 cents per minute up to a maximum of 1,000 minutes. Let C(m) be the cost in dollars of making m minutes of calls with a phone on this plan, for 0 ≤ m ≤ 1,000.

a. Write C(m) as a piecewise-defined function.

b. Sketch the graph of C.