Ans: A
$\begin{array}{rcl}
\dfrac{a}{x} + \dfrac{b}{y} & = & 3 \\
xy\times \left( \dfrac{a}{x} + \dfrac{b}{y} \right) & = & 3 \times xy \\
ay + bx & = & 3xy \\
bx – 3xy & = & -ay \\
x ( b-3y) & = & -ay \\
x & = & \dfrac{-ay}{b-3y} \\
x & = & \dfrac{ay}{3y-b}
\end{array}$
$\begin{array}{rcl}
\dfrac{a}{x} + \dfrac{b}{y} & = & 3 \\
xy\times \left( \dfrac{a}{x} + \dfrac{b}{y} \right) & = & 3 \times xy \\
ay + bx & = & 3xy \\
bx – 3xy & = & -ay \\
x ( b-3y) & = & -ay \\
x & = & \dfrac{-ay}{b-3y} \\
x & = & \dfrac{ay}{3y-b}
\end{array}$
