Answer
$A_m=3.98\times10^{-6}m^2$
Work Step by Step
$\frac{D_m}{d_i}=\frac{D_p}{d_i+d_0}$
$d_i=d_0$
$D_m=\frac{D_p}{2}$
$A_m=\pi \big(\frac{D_m}{2}\big)^2=\pi \big(\frac{D_p}{4}\big)^2=\pi \big(\frac{4.5\times10^{-3}m}{4}\big)^2$
$=3.98\times10^{-6}m^2$