Carolines hair is 7 inches long and grows up to 1/5 inch each month. Trinity's hair is 10 inches long and grows about 1/10 inch each month. How many months will it take for Carolines hair to be atleast as long as Trinitys hair? Define the variable.

Atourist boat is used for sightseeing in a nearby river. the boat travels 2.4 miles downstream and in the same amount of time, it travels 1.8 miles upstream. if the boat travels at an average speed of 21 miles per hour in the still water, find the current of the river.