If f(x+y)=f(x)+f(y)f(x+y) = f(x) + f(y)f(x+y)=f(x)+f(y) for all x,yx, yx,y and f(3)=12f(3) = 12f(3)=12, what is f(7)f(7)f(7)?
24
28
32
36