Obtain the amount of $_{27}Co^{60}$ necessary to provide a radio active source 0f $8.0\;mci$ strength. Half life of $_{27} Co ^{60}$ is $5.3$ years

Question

$\begin{array}{1 1} 7.12 \times 10^{-5}\;g \\ 7.12 \times 10^{5}\;g \\ 7.12 \times 10^{-6}\;g \\ 7.12 \times 10^{6}\;g \end{array}$