First we calculate the molecular weight of monomer $2,3,4-$tribromohexane

The atomic weights are approximately:

Carbon $($C$)$ : $12\mathrm{.}01\frac{g}{m}ol$

Hydrogen $(H)$:$1\mathrm{.}008\frac{g}{m}ol$

Bromine $($Br$)$ : $79\mathrm{.}904\frac{g}{m}ol$

Now, we calculate the molecular weight:

Molecular Weight $=(6C)+(11H)+(3Br)$

$MW=(612\mathrm{.}01\frac{g}{m}ol)+(111\mathrm{.}008\frac{g}{m}ol)+(379\mathrm{.}904\frac{g}{m}ol)$

$MW=72\mathrm{.}06\frac{g}{m}ol+11\mathrm{.}088\frac{g}{m}ol+239\mathrm{.}712\frac{g}{m}ol$

$MW$~~$323\frac{g}{m}ol$