The right answear is 1st one; Doing multiple trials will identify how much mistake you/material is doing. Replication is a must if you want it to be official.
The momentum is equal to m*v
m is mass
v is speed
so 1.5 kg*1.4m/s + 1 kg*1.4m/s
2.5kg*1.4m/s
3.5 kgm/s
hope it helps