\[ C(x)=\left\{\begin{array}{ll}19.99 & \text { if } 0250 \\ \text { monthly cost for a subscriber, where } x \text { is the number of anytime minutes used. }\end{array}\right. \] Compute the monthly cost of the cellular phone for use of the following anytime minutes. \( \begin{array}{lll}\text { (a) } 135 & \text { (b) } 325 & \text { (c) } 251\end{array} \) \( \begin{array}{ll}\text { (a) } C(135)=\$ \square \text { (Round to the nearest cent as needed.) }\end{array} \)

To calculate the monthly cost for each case, we will use the piecewise function provided. First, for 135 minutes: Since \( 0 < 135 \leq 250 \), we use the first piece of the function. \[ C(135) = 19.99 \] Thus, \( C(135) = \$ 19.99 \). Next, for 325 minutes: Since \( 325 > 250 \), we use the second piece of the function. \[ C(325) = 0.25 \cdot 325 - 42.51 = 81.25 - 42.51 = 38.74 \] Thus, \( C(325) = \$ 38.74 \). Finally, for 251 minutes: Since \( 251 > 250 \), we also use the second piece of the function. \[ C(251) = 0.25 \cdot 251 - 42.51 = 62.75 - 42.51 = 20.24 \] Thus, \( C(251) = \$ 20.24 \). In summary: (a) \( C(135) = \$ 19.99 \) (b) \( C(325) = \$ 38.74 \) (c) \( C(251) = \$ 20.24 \)