Correct Answer  Option 2 : 10 units
The correct answer is option 2) i.e. 10 units
CONCEPT:

Linear momentum: Momentum is defined as the impact due to a moving object.
Where m is the mass of the object and v is the velocity of the object.
 Linear momentum of a system of particles:
Let us consider a system of particles with each particle having a mass m and velocity v.
If p is the linear momentum of each particle, p = mv
Total linear momentum, Σp = Σmv = Σm . Σv = M.vcom
Where M is the sum of the mass of all particles, and vcom is the velocity of the centre of mass.
CALCULATION:
Given that:
p_{1} = 20î + 30ĵ + 40k̂ and p_{2} = 20î + 40ĵ + 60k̂
Velocity of the centre of mass, v_{com} = 4î + 5ĵ + 7k̂
Let M be the mass of the system.
We know that,
Σp = Mvcom
⇒ (20î + 30ĵ + 40k̂) + (20î + 40ĵ + 60k̂) = M (4î + 5ĵ + 7k̂)
Considering the x direction,
⇒ (20î) + (20î) = M(4î) (Mass is a scalar quantity.It will have no components in different directions)
⇒ 40î = M 4î
⇒ M = 10 units