Answer
$38.83$
Work Step by Step
Use the formula for average value with a=0 and b=5. The average price is: $\frac{1}{5-0}\int^{5}_{0}(t(25-5t)+18)dx=\frac{1}{5-0}\int^{5}_{0}((25t-5t^{2})+18)dx=\frac{1}{5}(\frac{25t^{2}}{2}-\frac{5t^{3}}{3}+18t)|^{5}_{0} \approx \frac{233}{6} \approx 38.83$