Find the missing measurements for each circle. Give your answers in terms of $\pi$.
a. The circumference is $2 \pi$ in., so the diameter is 2 in. The area is $A=\pi\left(2^{2}\right)=4 \pi$ in $^{2}.$
b. The circumference is $2 \pi$ in., so the radius is 1 in. The area is $A=\pi\left(1^{2}\right)=2 \pi \mathrm{in}^{2}.$