Jon P. answered 01/09/15
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First let's calculate the total volume of the water in the can. The formula is πr2h, where r is the radius and h is the height (or depth).
So that gives us a total volume of π*202*20 = 8000π cm3 (cubic centimeters).
So now let's add in the brick. That's going to increase the total volume of "stuff" in the can by 1500 cm3. So now the total volume is 8000π + 1500.
Now adding a brick is pretty much the same as adding water with the same volume. Adding the brick will push up the water around it, and adding water will basically do the same thing. So think of this can as having 8000π + 1500 cm3 of water. Let's write an equation that describes this:
V = πr2h
Since the radius is still 20, this becomes:
V = 400πh
Set this equal to 8000π + 1500, which is the new volume:
400πh = 8000π + 1500
Now solve for h:
h = (8000π + 1500) / 400π
h = (80π + 15) / 4π