Answer: 52 mph
Explanation:
Assume the following :
a = average speed traveled on level road
(a - 20) = average speed traveled on winding road
Recall:
Distance = speed × time
Total distance traveled :
Level road distance + winding road distance = 252 miles
3a + 3(a - 20) = 252
3a + 3a - 60 = 252
6a = 252 + 60
6a = 312
a = 52 mph on a level triad