Let $f(x)=2x-4$ and $g(x)=x^2+3$. What is $f(g(2))$?
To find $g(2)$, I just replace $x$ with $2$ in the expression for $g(x)$ and simplify. So, $g(2)=(2)^2+3=4+3=7$. Now, I have $f(g(2))=f(7)$. To find $f(7)$, I just replace $x$ with $7$ in the expression for $f(x)$ and simplify. So, $f(7)=2(7)-4=14-4=10$. Therefore, $f(g(2))=10$. 