Here is the problem:

Let f(x) = x^2 - 5. If f(6) - f(4) = f(y), what is the |y|?

I would appreciate if the work is explained because I need to explain this to my little sister. It has been so long since I've taken a math class that I feel pretty lost. I got 20 as my answer, but I know that it is wrong. The answer is supposed to be 5.

Thanks in advance.