<PRE><B>Question 1055332</B>
f(t)=6 sqrt(t).  That is the radius
The area is pi*r^2=pi*36t.  6 sqrt(t) squared is 6 squared* sqrt(t) squared,or 36 t.
A(t)=36t*pi m^2.
after 20 hours, the area is 720 pi m^2=2262 m^2.  Check with the radius, which is 6sqrt(20)=26.83 m
The area is 26.83^2*pi=2261.47, close enough with rounding.
850 m^2=36*pi*t
divide 850 by 36*pi=7.5 hours.
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Check
radius after 7.5 hours is 6*sqrt(7.5)=16.43 m
The area is pi*(16.43^2) m^2=848.05 m^2, close enough with rounding.</PRE>