Two railway wagons are connected by a coupling and move together along a straight, level track. The mass of one wagon is 12 000 kg12\,000\ \text{kg}12000 kg and the mass of the other is 18 000 kg18\,000\ \text{kg}18000 kg. The resultant horizontal force on the two wagons is 7500 N.
Calculate the acceleration produced by the resultant force on the wagons.