Answer:
The speed at which the buss made the trip was 45 mph and the train was 57 mph.
Explanation:
The average speed is given by:
speed = distance / time
Therefore we can manipulate it to give us the distance:
distance = speed*time
The time distance of each stage of his trip summed must be equal to the total distance of the trip. Since he made a trip in two legs, one by bus that lasted 3 h at a speed of "x" and one that lasted 5 hours at a speed of "x + 12". We have:
420 = 3*x + 5*(x + 12)
3*x + 5*(x + 12) = 420
3*x + 5*x + 60 = 420
8*x = 420 - 60
8*x = 360
x = 45 mph
The speed at which the buss made the trip was 45 mph and the train was 57 mph.