If $\tan A-\tan B=x$ and $\cot B-\cot A=y$ then $\cot(A-B)$ is equal to

Question

$\begin{array}{1 1}(a)\;\large\frac{1}{y}-\frac{1}{x}&(b)\;\large\frac{1}{x}-\frac{1}{y}\\(c)\;\large\frac{1}{x}+\frac{1}{y}&(d)\;None\;of\;these\end{array}$