functions help.....

Consider the function g(x)=3x-4. 

For what value of  a  is g(a)=0 ?

$g(a) = 0:$

$\begin{array}{|rcll|} \hline g(a)= 0 &=&3a-4 \\ 0&=& 3a-4 \quad & | \quad +4 \\ 4&=& 3a \quad & | \quad :3 \\ \dfrac{4}{3} &=& a \\ \mathbf{ a } &\mathbf{=}& \mathbf{ \dfrac{4}{3} } \\ \hline \end{array}$