Question 259198
f(g(x)) means wherever there is an x in f, substitute g(x).
{{{f(x)=2x+3}}}

{{{f(g(x))=2(g(x))+3=2(3x-4)+3}}}
{{{f(g(x))=6x-8+3}}}
{{{f(g(x))=6x-5}}}