EtBr+Zn--> Butane
Butane-(radical halogenation& isomer separation)-->1-chloro butane (or start with methanol and do successive SOCl2, Mg, CH2O treatments till you get butanol and 1-chlorobutane lol)
BnOH-->BnCl
BnCl--(1.grig, 2. CH2O)-->Ph-CH2-CH2-OH--(SOCl2)-> Ph-CH2CH2-Cl
PhCH2CH2Cl--(Mg)-->PhCH2CH2MgCl--(Acetaldehyde)-->PhCH2CH2C(OH)CH3--(ox)-->PhCH2CH2C(O)CH3
BuCl-(Mg)->BuMgCl--(PhCH2CH2C(O)CH3)--> product.
But really, lots of different routes. Above reactions are all just intro ochem to keep things simple.