2016 IJC Promo Q3

At the beginning of an experiment, an inverted circular cone is filled with sand. The base radius of the cone is \(5\) cm and the slant height is \(13\) cm. Sand is leaking through a small hole at the bottom of the cone at the rate of \(7\) cm\(^{3}\)s\(^{-1}\) at the instant when the depth of the sand in the cone is \(2.5\) cm. Find the rate of decrease of the depth of the sand at this instant.[5]