If the alexanders completed the 735 mile trip in 15 hours, what was their average rate of travel?

The rate of travel here is in mph - "miles per hour".

That just means how many miles you can travel in one hour. In this problem, you're given 15 hours, and the distance they travel within those 15 hours.

Therefore, you should divide both the number of miles and the number of hours by 15 to find out how far they can travel in 1 hour.

735 ÷ 15 = 49 miles
15 ÷ 15 = 1 hour

Their average rate of travel was 49 miles in 1 hour, which is 49 mph.

First, divide 735 by 15 which equals 49.
Then 15 by 15 equaling 1.

So, the answer would be:
49 miles per hour