In the figure given above, $DE||BC$, where $AE=a, \; DA=b$ and $DE=x$ and $BC=y$. Express $x$ in terms of $a,b$ and $y$
$\begin{array}{1 1} (a)\; x=\large\frac{ab}{a+y} \\ (b)\; x=\large\frac{by}{a+b} \\ (c)\; x=\large\frac{ab}{a+y} \\ (d)\; x = \large\frac{ay}{a+b } \end{array}$
