CAP 697 MRJT FIG 4.4

FINAL RESERVE fuel is calculated (for a turbojet) as 30 mins fuel at 1500ft above DESTINATION ALTERNATE....hence your calculation is correct...destination alternate is at 30ft amsl, so you need 30 mins fuel at 1530ft (mass 50000kgs).

From the table – fuel flow 2280 kg/hr, so FINAL RESERVE = 1180 kgs

They have offered destination airfield elevation as a distraction - its irrelevant!