Answer:
\(f(x)=\left\{\begin{array}{l}19,\ \ x\le 300\\ \\19+0.39(x-300),\ \ x>300\end{array}\right.\)
Step-by-step explanation:
Andrew has a cell phone plan that provides 300 free minutes each month for a flat rate of $19. For any minutes over 300, Andrew is charged $0.39 per minute.
Let x be the number of minutes Andrew uses per month and f(x) be the charges based on Andrew's cell phone plan.
If \(x\le 300,\) then \(f(x)=19.\)
If \(x>300,\) then first 300 minutes are free and each minute of next (x-300) minutes costs $0.39, therefore
\(f(x)=19+0.39(x-300).\)
Hence,
\(f(x)=\left\{\begin{array}{l}19,\ \ x\le 300\\ \\19+0.39(x-300),\ \ x>300\end{array}\right.\)
