__Evaluate f(g(x))__

f(g(x)) = 3(x^2 + 2x) + 1

f(g(x)) = 3x^2 + 6x + 1

__When f(g(x)) = 10, we have__

10 = 3x^2 + 6x + 1

__Subtract 10 from each side:__

3x^2 + 6x - 9 = 0

Divide each side of the equation by 3

x^2 + 2x - 3 = 0

Factor, we have: (x + 3)(x - 1) = 0

So x is either

**1 or -3**