Answer :
Given the following functions:
[tex]\begin{gathered} f(x)=x^2 \\ g(x)=3x-1 \end{gathered}[/tex]To compose then, is basically use the inside function as the argument.
[tex]f(g(x))=f(3x-1)[/tex]If we call '3x-1' as 'u'
We know the following
[tex]\begin{gathered} f(u)=u^2 \\ u=3x-1\Rightarrow f(3x-1)=(3x-1)^2 \end{gathered}[/tex]And this is our answer.
[tex]f(x)=(3x-1)^2[/tex]