Although they are the same variable, you cannot add two variables raised to different powers. 3x^1 + 5x^2 cannot work, but 3x^2 + 5x^2 can. Also, if you are multiplying them, they would combine to be 15x^3, as 3 and 5 (The coefficients) multiply together and x^2 times x^1 = x^3.
I hope that helps.
The answer is (f o g)(x) = 2x^2 - 13
In order to find a composite function, you take the first letter (in this case f) and use that equation. You then remove the variable and put in the second letter (g).
f(x) = 2x + 1 ----> Remove variable.
f(x) = 2( ) + 1 ----> Insert g(x)
(f o g)(x) = 2(x^2 - 7) + 1 ----> Distribute
(f o g)(x) = 2x^2 - 14 + 1 ----> Simplify
(f o g)(x) = 2x^2 - 13
It is the first one, so where it is marked is already correct
It should be C., is that what the graph looks like?