Chemical Kinetics

Consider the reaction

\(3 \mathrm{I}_{(\mathrm{aq})}^{-}+\mathrm{S}_2 \mathrm{O}_{8(\mathrm{aq})}^{--} \longrightarrow \mathrm{I}_{3(\mathrm{aq})}^{-}+2 \mathrm{SO}_{4(\mathrm{aq})}^{2-}\)

rate of formation of $\mathrm{SO}_4^{2-}$ at a particular time is

\(2.2 \times 10^{-2} \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{~s}^{-1}\)

What is the value of $\frac{d}{d t}\left[I_3^{-}\right]$?