Here is a calculus question I'm apparently struggling with.
A plane flying horizontally at an altitude of $2~\mathrm{mile}$ and a speed of $520~\mathrm{mile\ h^{-1}}$ passes directly over a radar station. Find the rate at which the distance from the plane to the station is increasing when it is $5~\mathrm{mile}$ away from the station. (Round your answer to the nearest whole number.)
I used the equation $z^2$=$x^2$=$y^2$ and found $z=\sqrt{ 29}$, and $\frac{dz}{dt}$=$\frac{2600}{\sqrt{29}}$ which is $483~\mathrm{mile\ h^{-1}}$, but web assign claims its wrong. Am I mistaken somewhere? Thanks!