Answer:
6000π m²/h
Step-by-step explanation:
Area of the circular cloud =πr²----------------------------------------- (1)
Radius as a function of time = R(t)=50+20t------------------------ (2)
dA/dt = (dA/dr) x (dr/dt)-----------------------------------------------------(3)
dA/dr = 2πr
dr/dt = 20
After 5 hours, the radius of the cloud will be :
R(5)=50+20(5)
= 150 meters
Substituting into (3)
dA/dt = 2π(150) x 20
= 6000π m²/h
