Question 327079
There are various ways to set this up. 

Use d=rt.

The first part of the trip is 76 miles, so we have rt=76.

Since the entire trip took 4 hours, the second part took 4-t hours.

The second part was 5 mph slower, so we have (r-5)(4-t)=20

From the first part, we have t=76/r.

Sub into the second one:

(r-5)(4-(76/r))=20

Solving this we have r=25.24 and 3.76

3.76 is extraneous, so we go with 25.24 mph as the rate on the first part and 20.24 on the second part.