Let the moving object be object 1 and the stationary object be object 2.
Momentum of object 1 before collision = 55 kg*m/s
Momentum of object 2 before collision = 0 kg*m/s
Momentum of object 1 after collision = 13 kg*m/s
According to the law of conservation of momentum, the sum of the momenta of 2 objects remains the same even after collision. So,
Momentum of object 1 before collision + momentum of object 2 before collision = Momentum of object 1 after collision + momentum of object 2 after collision
55 + 0 = 13 + momentum of object 2 after collision
Momentum of object 2 after collision = 55 - 13 = 42 kg*m/s
Hope I helped!
