# Chapter 1 - Section 1.2 - Basics of Functions and Their Graphs - Exercise Set - Page 180: 132

We get the value of $C\left( 100 \right)=\$36$. #### Work Step by Step$C\left( t \right)=20+0.4\left( t-60 \right)$Where$C\left( t \right)$is the monthly cost in dollars and$t$is calling minutes. For$t=100$:$\begin{align} & C\left( 100 \right)=20+0.4\left( 100-60 \right) \\ & =20+0.4\left( 40 \right) \\ & =20+16 \\ & =36 \end{align}$Thus, for 100 calling minutes, the monthly cost is$36.

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