Answer: 1 m/s to the left
Step-by-step explanation: Considering momentun conservation, this is as follow:
PA+PB= Constant
PA= 2 Kg * 4 m/s to the rigth
PB= 5 Kg* 3 m/s to the left
after collision the two mass go together so the PA+B = Vfinal (mA+mB)= Vfinal (2 kg +5 kg), the momentum conservation is then
PA-PB=8-15=-7 = Vfinal (7kg)
Vfinal= -7/7 m/s=-1 m/s