I have three problems I am stuck on and can't figure them out.

The first deals with functions and the book comes up with the answer of 1 but I think i am losing my hair now trying to get that.

f(3)+g(3)

the next one is solving the variables by using the addition method

3x-4y+4z=7

x-y-2z=2

2x-3y+6z=5

the next is using cramer's rule

3x=7y+1

2x=3y-1