23) A
Total mass of the train = 20000 + 5000 + 5000 = 30000 kg
Ratio of masses = 20000 : 5000 : 5000 = 4 : 1 : 1
Initial thrust = 15000 N
Total parts in the ratio above = 4 + 1 + 1 = 6
15000 ÷ 6 = 2500N
Thrust on engine = 2500 x 4 = 10000 N
Thrust on individual carriage = 2500 x 1 = 2500 N
So A is the answer.