Partial Derivatives & the Gradient · Hard problem

A firm's output is $P(x,y) = 60\sqrt{x}\,\sqrt[3]{y}$, where $x,y>0$ are units of two inputs. At the current input levels $(x,y)=(9,8)$, decide whether one more unit of $x$ or one more unit of $y$ increases output more (approximately), and report the SIZE of that larger increase.