If f(x)=x2f(x) = x^2f(x)=x2 and g(x)=x+3g(x) = x+3g(x)=x+3, which expression represents g(f(x))g(f(x))g(f(x))?
x2+3x^2 + 3x2+3
(x+3)2(x+3)^2(x+3)2
x2+6x+9x^2 + 6x + 9x2+6x+9
3x23x^23x2