The reaction of 4-methyloct-1-ene (P, 2.52 g) with HBr in the presence of (C₆H₅CO)₂O₂ gives two isomeric bromides in a 9:1 ratio, with a combined yield of 50%. The entire amount of the primary alkyl bromide was reacted with an appropriate amount of diethylamine followed by treatment with aqueous K₂CO₃ to give a non-ionic product S in 100% yield. The mass (in mg) of S obtained is ___.