If the area of $\triangle ABC$ is 225 and $AB=17$, then what is the value of $\cos x$ ?

Question

$\begin{array}{1 1} (a)\;\large\frac{8}{17} \\ (b)\;\large\frac{8}{15} \\ (c)\;\large\frac{17}{30} \\ (d)\;\large\frac{15}{17} \end{array}$