Ans: $y = \dfrac{3x}{k+1} $
$\begin{array}{rcl}
k & = & \dfrac{3x-y}{y} \\
ky & = & 3x – y \\
ky + y & = & 3x \\
y (k+1) & = & 3x \\
y & = & \dfrac{3x}{k+1}
\end{array}$
$\begin{array}{rcl}
k & = & \dfrac{3x-y}{y} \\
ky & = & 3x – y \\
ky + y & = & 3x \\
y (k+1) & = & 3x \\
y & = & \dfrac{3x}{k+1}
\end{array}$
