Aboat travels 36 miles in 1.5 hours ans then in 14 miles in 0.75 hour. what is the average speed?

36 miles in 1.5 hours means x miles in 1 hour. We divided 1.5 hours by 1.5 to get 1 hour, so we have to also divide 36 miles by 1.5 to find the distance travelled in 1 hour:

36 / 1.5 = 24 [miles per hour]

In the second situation:

0.75 hour / 0.75 = 1 hour
14 miles / 0.75 = 18,(6)       (infinite number of 6s - repeating decimal)

So here the boat travelled at the speed of about 18,7 miles per hour.

To find the overall average speed we have to add both speeds and then divide it by 2:

24 + 18,7 = 42,7
42,7 / 2 = 21,35

The average speed of the boat was 21,35 miles per hour.

The answer to your question is b