Chemical Kinetics

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