Chemical Kinetics

Consider the reaction $3 \mathrm{I}^{-}+\mathrm{S}_2 \mathrm{O}_8^{2-} \longrightarrow \mathrm{I}_3^{-}+2 \mathrm{SO}_4^{2-}$, at a particular time t , $\frac{\mathrm{d}\left[\mathrm{SO}_4^{2-}\right]}{\mathrm{dt}}$ is $2.2 \times 10^{-2} \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{~s}^{-1}$. What is the value of $\frac{\mathrm{d}\left[\mathrm{S}_2 \mathrm{O}_8^{2-}\right]}{\mathrm{dt}}$ ?