Which reagent sequence converts $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{Br}$ into propan-1-amine, $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{NH}{}_2$?

One carbon must be added. KCN gives $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CN}$ (C-attack), and LiAlH4 reduces it to $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{NH}{}_2$. AgCN is covalent and gives the isocyanide $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{NC}$, whose reduction gives the secondary amine $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{NHCH}{}_3$. Gabriel synthesis and ammonolysis give ethylamine (no carbon added).