[tex]y\text{ = 2a-2}[/tex]
Here, given the equation in the question, we want to make y the subject of the formula;
[tex]\begin{gathered} \frac{2}{a-1}=\frac{4}{y} \\ \\ 2\text{ }\times\text{ y = 4(a-1)} \\ \\ 2y\text{ = 4a-4} \\ \\ 2y\text{ = 2(2a-2)} \\ \\ y\text{ = 2a-}2 \end{gathered}[/tex]
