So if boys is 6 and girls is 15 it would be 6/15, but that can be simplified to 2/5.
Yes it has a constant rate of change which is 3/2
First you would have to find the distance it's going per hour.

You will then get the answer of 200 m/hr. You can then plug in 200 m/hr to find how far the jet could fly in 10 hours

You're final answer should be 2,000 miles