At t = 0, a car registers at 30 miles/hr. Forty seconds later, the car’s velocity is now at 50 miles/hr. Assuming constant acceleration, find the value of this acceleration. Select one:
a. 20 miles/hr2
b. 0.5 miles/hr2
c. 0.5 miles/s2
d. 1.38 x 10-4 miles/s2
e. None of the given choices.