# Rates and derivates

I've found this question but don't really understand it, I don't know if i'm missing something or if it is in fact badly worded, any suggestion will help, thanks:

A man walks on a straight line. A spotlight, located on the ground 100m from the path of man, keeps the focus on him. If the spotlight turns at a rate of 0.002 rounds per minute, which is the speed of the man when he is at 125m from the spotlight?

Hint: Let $D$, $x(t)$ and $y(t)$ be the catheti and the hypotenuse. $$D^2 + x(t)^2 = y(t)^2$$ Find the derivatives of the equation with respect to $t$. Use that $\sin(\theta(t)) = \frac{x(t)}{y(t)}$, $\cos(\theta(t)) = \frac{D}{y(t)}$ and solve for $x(t)$.