(c) $i = 6.6 \times 10^{15} \times 1.6 \times 10^{- 19} = 10.5 \times 10^{- 4}amp$
$A = \pi R^{2} = 3.142 \times (0.528)^{2} \times 10^{- 20}m^{2}$
$\Rightarrow M = iA = 10.5 \times 10^{- 4} \times 3.142 \times (0.528)^{2} \times 10^{- 20}$
$= 10 \times 10^{- 24}units = 1 \times 10^{- 23}units$