smc

Suppose that Sam's average speed during the last $30$ minutes was $x$ mph. Recall that a half hour is equal to $30$ minutes. Therefore, Sam drove $60\cdot 0.5=30$ miles during the first half hour, $65\cdot 0.5=32.5$ miles during the second half hour, and $x\cdot 0.5$ miles during the last half hour. We have $$\begin{array}{rl}30+32.5+x\cdot 0.5& =96\\ x\cdot 0.5& =33.5\\ x& =\boxed{67}.\end{array}$$