Again referring to the diagram above (click on it for a better view) we see that the distance that the hawk has flown in time $t$ is given by the integral $\int_c^d F dx$ where
$c$ =
$d$ =
(Hints: Note that this integral computes the length of a curve. Also recall that the hawk's initial position is at $(a,0)=(6000,0)$. )
and
$F$ =
(Use $p$ to denote $\frac{dy}{dx}$ in your last answer above.)

On the other hand the hawk is flying at a constant speed of 20 for time $t$. Hence the total distance it has flown is . If we equate this to the distance we just computed and solve for $t$ we obtain $$t = \int_c^d G dx$$ where $G$ =
(Remember to use $p$ to represent $\frac{dy}{dx}$.)