NAM = NGM x (TAS/GS) = 4000 x (450/400) = 4500 NAM

FPR = (Departure price/Destination price) = 0.27/0.30) = 0.90

Enter graph 0.90 FPR → 4500 NM ↓ OPTIMUM WEIGHT = 178 000 kg

TOM 170 000 kg, no other limits, so TANKER 8 000kg