Some rough figures
Max reverse thrust on 744 RR is about 80% of takeoff thrust, therefore your reverse thrust fuel consumption
would be approx (round figures only) 80% of takeoff fuel burn
7800 kgs per hr at T.O. x 80% = 6240 kgs per hour = 104 kgs per min
20 secs of full reverse = 35 kgs of fuel for a full power reverse landing
4 engines x 35kgs = 140 kgs
All figures are from engine run memory so please excuse me if the T.O. figures are out
Regards
Bolty