Answer: The average speed on the afternoon route is 40 miles per hour.
Explanation:
Let the average speed of afternoon route be 'x'.
Let the average speed of morning route be 'x-12'.
Distance covered on the morning route = 70 miles
Distance covered on the evening route = 100 miles
Since they take the same amount of time.
So, our equation becomes,
![(70)/(x-12)=(100)/(x)\\\\70* x=100(x-12)\\\\70x=100x-1200\\\\1200=100x-70x\\\\1200=30x\\\\x=(1200)/(30)\\\\x=40](https://img.qammunity.org/2020/formulas/mathematics/middle-school/nhn7jwd9adgt6ajisx2hy5lg5izkxelex8.png)
Hence, the average speed on the afternoon route is 40 miles per hour.