Someone helped me solve this but then i saw the "t = 1" so i dont think it works anymore...

hear is the question:
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=20/sqrt(t), t = 1, 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

Hear is my awnser
1=40*sqrt(0.25)+c
so c = 1
r=40*sqrt(t)+1
r=40*sqrt(10)+1=127.491
nerest meter is 127

Question

Someone helped me solve this but then i saw the "t >= 1" so i dont think it works anymore...

hear is the question:
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=20/sqrt(t),    t >= 1, 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

Hear is my awnser
1=40*sqrt(0.25)+c
so c = 1
r=40*sqrt(t)+1
r=40*sqrt(10)+1=127.491
nerest meter is 127