V = Volume of cylinder
B = area of base
h = height of cylinder
It turns out that
V = B*h
In a similar way to that of a cube
If we know that V = 84pi and h = 7, then we can plug those values into the formula above, and solve for B
V = B*h
84pi = B*7
84pi/7 = B*7/7 ... divide both sides by 7
12pi = B
B = 12pi
Therefore the base is 12pi square units