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the water level rises by 0.025ft each min

Step-by-step explanation:

The volume of a rectangular fish tank is:

V = height*base

then if the hwight is 1 ft, we have that the volume is:

V = 1ft*20ft^2 = 20ft^3

Now, the amount of water that enters in the tank is r = 0.5ft^3/min

now, the change in the heigth will be

change in volume = r =change in height*base

r/base = height.

(0.5ft^3/min)/20ft^2 = change in height = 0.025ft/min

This means that the water level rises by 0.025ft each min