15. $\triangle A B C$ is a right-angled triangle with $\angle A B C=90^{\circ}$. A circle $C_{1}$ is drawn with $A B$ as diameter, and another circle $C_{2}$ is drawn with $B C$ as diameter. The circles $C_{1}$. and $C_{2}$ meet at the points $B$ and $P$. If $A B=5 \mathrm{~cm}, B C=12 \mathrm{~cm}$ and $B P=x \mathrm{~cm}$, find the value of $\frac{2400}{x}$.