CnH2n-6
%H=2n-6/14n-6*100 => 8,69 = (2n-6)/(14n-6)*100 ==> 121,66n-52,14 = 200n-600 => 78,34n = 547,86 => n=7
F.M => C7H8 -> C6H5-CH3 [A]
C=37/12 = 3,083 => 2,333 atomi C
H=2,2 => 1,6654 atomi H
N=18,5/14 = 1,321 =< 1 atom N
O=42,29/16 = 2,643 => 2 atomi O
F.B => (C2,333H1,6654NO2)n => pt n=3 => C7H5N3O6
C6H2-CH3 (NO2)3 -> trinitrotoluen