This problem can be solved using the formula
D = rt
Where d is the distance
R is the speed
T is the time
Then establish the two equation
D = 50t
D = 40(t+3)
Equating the two quations
50t = 40(t+3)
T = 12 hrs he took to drive from alentown to baker
D = 50x12 = 600 miles