For this, all you have to do is create equations where all you have to do is change the x value. The equation for gym A would be 35 + 42x, where x is the number of months he has the membership, and the first number is the initial fee. The equation for gym B would be 65 + 36x, following the same rules. Now all you have to do is set both of these equations equal to each other:
65+36x=35+42x
Solving this equation results in x=5, which means that he has to have the memberships for 5 months for them to be equal. Now just plug that in to one side of the equation to get the amount he has to spend:
65+36(5) = $245
Without speeding up it would take 5 1/3 seconds.. not sure if it speeds up in the question?
The independent variable is the variable that is being changed. In this statement, it would be water flowing flowing in the pool. The dependent variable is what is being changed so that would be the depth of the water.
There, I hope this helps! :)