## Elementary Algebra

We know that for a function, $f(x)$, $f(a)$ tells us to find the value of $f$ when $x=a$. Thus, for $f(x)=3x+4$, $f(7)$ means that we need to substitute $x=7$ in the function to find the value of $f$ when $x=7$. Therefore, the statement is true.