Enthalpy of hydrogenation of cyclohexene =−28.6 kcal/mol
∴ Calculated enthalpy of anthracene =−28.6×7=−200.2 kcal/mol
(As there are 7 double bonds in anthracene)
Hence, Resonance energy = Calculated enthalpy- Actual enthalpy
=−200.2−(−116.2) kcal/mol
=−84 kcal/mol
Therefore, magnitude of x is 84.