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.