D. \( f(x)=\left\{\begin{array}{ll}4.10+0.05747 x & \text { if } x \leq 1500 \\ 90.305+0.03788(x-1500) & \text { if } x>1500\end{array}\right. \) b) What is the monthly charge if 980 kWh are used? \( \$ \square \) (Type an integer or a decimal rounded to two decimal places as need

To find the monthly charge for using 980 kWh, we need to use the first part of the piecewise function since 980 is less than or equal to 1500. Using the formula \( f(x) = 4.10 + 0.05747 x \): \[ f(980) = 4.10 + 0.05747 \times 980 \] Calculating \( 0.05747 \times 980 \) gives: \[ 0.05747 \times 980 = 56.3306 \] Now plug that back into the equation: \[ f(980) = 4.10 + 56.3306 \approx 60.43 \] Therefore, the monthly charge for using 980 kWh is approximately \( \$60.43 \). So the final answer is: \( \$60.43 \)