Multi-step integrative calculation and reasoning: A person maintains weight at 1,800 kcal/day. They add a 700 kcal/day surplus for 8 weeks and start resistance training; measured changes: +1.5 kg lean mass (via DEXA) after 8 weeks. Using 7,700 kcal/kg as the energy equivalent of gained tissue, estimate the fat mass gained (kg). Show all steps and justify whether the observed change in body composition is consistent with the energy surplus.