Answer:
d. 69.8 mph
Step-by-step explanation:
Since, the ratio of the diameter of the tyre of a vehicle and its speed must be constant,
Given,
The original diameter of the tyre = 29 inch,
Original speed = 60 mph,
Thus, the ratio of diameter and the speed of the vehicle = 
New diameter of the tyre = 33.73 inch,
Let x be the new speed of the vehicle = 


Hence, the actual speed of the vehicle would be 69.8 mph.
OPTION D is correct.