${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{COO}}^{-}{\mathrm{Na}}^{+}\underset{\mathrm{Heat}}{\overset{\mathrm{NaOH},+?}{\to }}{\mathrm{CH}}_3{\mathrm{CH}}_3+{\mathrm{Na}}_2{\mathrm{CO}}_3$
Consider the above reaction and identify the missing reagent/chemical