First we need to find the radius of the cylindrical tree trunk if the circumference C=4 feet: C=2rπ, r=4/(2π)=2/π. Now we find the volume V: V=r^2π*h, where h=20 feet is the height. So we input the numbers: V=(2/π)^2*π*20=(4/π²)*π*20. π in the nominator and the denominator cancel out: V=(4/π)*40=80/π. The volume of the cylindrical tree trunk is V=80/π feet^3
