Write the Word or Phrase That Best Completes Each Statement

Write the word or phrase that best completes each statement or answers the question.
-A cellular phone plan had the following schedule of charges: $\begin{array}{ll}\text { Basic service, including } 100 \text { minutes of calls } & \$ 20.00 \text { per month } \\2 \text { nd } 100 \text { minutes of calls } & \$ 0.075 \text { per minute } \\\text { Additional minutes of calls } & \$ 0.10 \text { per minute }\end{array}$ What is the charge for 200 minutes of calls in one month?
What is the charge for 250 minutes of calls in one month?
Construct a function that relates the monthly charge C for x minutes of calls.