From 200mg of $CO_2,10^{21}$ molecules are removed.How many moles of $CO_2$ are left?

Question

$\begin{array}{1 1}(a)\;3.1\times 10^{-3}&(b)\;2.4\times 10^2\\(c)\;2.88\times 10^{-3}&(d)\;2.88\times 10^{-7}\end{array}$