Benzene is treated in sequence with (i) CH3COCl/anhyd. AlCl3, (ii) Br2/FeBr3, and (iii) Zn-Hg/conc. HCl. The final major product is

Friedel-Crafts acylation gives acetophenone. The acetyl group is a meta-directing, deactivating group, so bromination gives 3-bromoacetophenone. Clemmensen reduction ($\mathrm{Zn\text{-}Hg/HCl}$) converts $\mathrm{C{=}O}$ to $\mathrm{CH_2}$, giving 1-bromo-3-ethylbenzene. Doing the reduction first would make the ethyl group ortho/para-directing and give the 4-bromo isomer; this is why the order of steps matters (acylation, then halogenation).