What can a denominator never be?
0
so, we need to figure what x can't be... the only way to multiply 2 things together to get 0 is if one or both are zero.
so, what x values make our denominator 0?
to figure this out, we need to set (x-1)(x-2)=0
now we split and solve.

so when x is 1 or 2 the function doesnt make sense.
but, x can be every other number and it does, so the answer is
ALL REAL NUMBERS not equal to 1 or 2
Its true for integers if you are using the associative property in addition or multiplication ONLY.
G(4)=7(4)+4
G(4)=28+4
G=32
F(32)= 3(32)^2
F= 9216
f(g(4))= 9216
13 and -3
13+-3=10
13x-3=-39