Mathematics
OpenStudy (anonymous):

An oil tanker aground on a reef is losing oil and producing an oil slick that is radiating out at a rate approximated by the function dr/dt , where r is the radius of the circular slick in metres after t minutes. If the radius of the slick is 21 metres, after 15 seconds, find, to the nearest metre, the radius of the slick after 10 minutes.

OpenStudy (anonymous):

$dr/dt = 20/\sqrt{t}$ when $t \ge1$ and r is the radios after t mins