#### Answer

$37.5$ miles per hour

#### Work Step by Step

Let $t_1$ be the time is taken for the forward trip:
Then, $t_1=\dfrac{150}{30}=5 hrs$
Let $t_2$ be the time is taken for the return trip:
Then, $t_2=\dfrac{150}{50}=3 hrs$
Now, $t_1+t_2=8 hrs$
Total distance =150 +150=300 miles
Thus, the total time taken is: $T=\dfrac{300}{8}=37.5$ miles per hour