Answer
a) $fog(x)=3x^2+3x+5$
b) $gof(x)=9x^2+33x+30$
c) $fof(x)= 9x+20$
d) $gog(x)=x^4+2x^3+2x^2+x$
Work Step by Step
a) $fog(x)=f(g(x))=3(g(x))+5=3x^2+3x+5$
b) $gof(x)=g(f(x))=(f(x))^2+f(x)=9x^2+33x+30$
c) $fof(x)= f(f(x))=3f(x)+5=9x+20$
d) $gog(x)=g(g(x))=(g(x))^2+g(x)=x^4+2x^3+2x^2+x$
