The hydrogen bromide addition in peroxides follows Anti Markovnikov rule. Anti Markovnikov addition reaction is found to follow a free radical mechanism. The peroxide compound involved helps in the generation of free radicals. The Anti-Markovnikov rule defines regiochemistry in which the substituent is attached to a less substituted carbon instead of the more substituted carbon.
The reaction of 3−Methylhex-2-ene with HBr in presence of peroxide, takes place as follows,

2 chiral carbons, here, so, total number of stereoisomers will be 2n=22=4