Organic compound $A+{\text{NH}}_3\to B\stackrel{\Delta }{\to }C\stackrel{{\text{Br}}_2/\text{KOH}}{\to }\text{ethylamine}$. Compound $A$ is:

The last step is Hoffmann Bromamide degradation, which converts an amide to an amine with one less carbon.Ethylamine (${\text{C}}_2$) $⟹$ Amide $C$ is Propanamide (${\text{C}}_3$).Amide $C$ comes from Ammonium salt $B$ (Ammonium propanoate), which comes from Acid $A$ (Propanoic acid).