The table gives the values of a continuous function $f$. $$\begin{array}{|c|c|c|c|c|c|c|c|}\hline x & 20 & 25 & 30 & 35 & 40 & 45 & 50 \\ \hline f(x) & 42 & 38 & 31 & 29 & 35 & 48 & 60 \\ \hline \end{array}$$ Use the Midpoint Rule to estimate the average value of $f$ on [20, 50].

Midpoint Rule estimate =