Find the area of this isosceles triangle ABC shown below, where $AB =15\;m$ and $BC= 20\;m$ and $\angle ABC=60^{\circ}$. Then the

Question

$\begin{array}{1 1} (a)\;225 \sqrt 3 m^2 \\ (b)\;\large\frac{225 \sqrt 3}{2}m^2 \\ (c)\;\large\frac{225 \sqrt 3}{4}m^2 \\ (d)\;\large\frac{225 \sqrt 3}{8}m^2 \end{array}$