First of all, the average speed is the ratio between the distance traveled and the time elapsed. So, the average speed of a car that travelled 720 kilometers in 6 hours is
kilometers per hour.
As for the second exercise, you can simply write this proportion:
Because we expect the distance traveled in 3 hours to be proportional to the distance traveled in 2 hours, if the (average) speed is the same.
The answer is 40. Your remainder must be less than the divisor. If you divide by 8 it would be 7 If you divide by 32 is would be 31 and so on. 40 is the greatest whole number less than 41