hi please i have to hand my assignment in by tomorrow and i don't know how to get started on some of the questions

1) if f(x) = x^2 + 5, find f(x+1) - f(x)

I have no idea how to even begin here

2) Find the domains of the following functions.

a) f(x) = 2x-37, do we just find a value for which the equation equals zero so x can be any real number except that one?

3) divide 3a^2/ a^2 - b^2 by a/ a + b

thanks i really need help quickly with question 1 and 3