Answer and when you answer explain how to do the problem and the work that comes with it. i just want to really understand how to do it

The answer is B.

In these type of questions there is a stable and non-changeable value. In this case, it is "a ONE-TIME fee of $75". It is the value which doesn't get effected by the variables.

Then there is the changing value which is the monthly fee. It is subject to the changes caused by the variable.

In order to construct this equation first take the one-time fee of 75, then add the monthly fee. And because the monthly fee is changing according to the months, we need to multiply the 25 with "m" which is the number of months passed.

So our equation is: