# How do you find the value of f(a), if f(x)=3x-4?

To find $f \left(a\right)$ substitute $\textcolor{red}{a}$ for each occurrence of $\textcolor{red}{x}$ in $f \left(x\right)$:
$f \left(\textcolor{red}{x}\right) = 3 \textcolor{red}{x} - 4$ becomes:
$f \left(\textcolor{red}{a}\right) = 3 \textcolor{red}{a} - 4$