The value of 30^ - 75^ 15^ - 60^ is?

Answer: Option D

$$\begin{array}{rl}& \frac{\cot {30}^{\circ }-\cot {75}^{\circ }}{\tan {15}^{\circ }-\tan {60}^{\circ }}\\ & =\frac{\tan {60}^{\circ }-\tan {15}^{\circ }}{\tan {15}^{\circ }-\tan {60}^{\circ }}\\ & =\frac{-\left(\tan {15}^{\circ }-\tan {60}^{\circ }\right)}{\tan {15}^{\circ }-\tan {60}^{\circ }}\\ & =-1\end{array}$$