We know that
1 quarter gallon of paint ⇄ 1/12 wall
?? ⇄ 1 wall
Now we just divide both sides of the equivalence
[tex]\begin{gathered} \frac{1}{?}=\frac{\frac{1}{12}}{1} \\ \frac{1}{?}=\frac{1}{12} \end{gathered}[/tex]We clear the equation in order to find the unkown value
[tex]\begin{gathered} \frac{1\cdot12}{1}=\text{?} \\ 12=\text{?} \end{gathered}[/tex]