The reaction of 4-methyloct-ene (P, 2.52 g) with HBr in the presence of ${\left(C_6{H}_{5}CO\right)}_2{O}_2$ gives two isomeric bromides in a 9:1 ratio, with combined yield of 50%. Of these, the entire amount of the primary alkyl bromide was reacted with an appropriate amount of diethylamine followed by treatment with eq. $K_{2}C{O}_3,$ to given a non-ionic product S in 100% yield. The mass (in mg) of S obtained is ______. [Use molar mass (in g $mo{l}^{-1}$ ): H=1,C= 12, N= 14, Br = 80]