Two identcal spiral galaxies A and B w/ equal & opposite momenta merge

[ritwik06]

Two identcal spiral galaxies A and B with equal but opposite momenta a and b are merged to form a resultant galaxy C with a net linear momentum c. Which is true?
a) c>b
b) 0<c<b
c)c= abs(b)+abs(a)
d) c=0

 

[SpaceTiger]

As usual, you need to show work.

 

[ritwik06]

As usual, you need to show work.

Well, this question came in my olympiad. If I had got it, i wouldn't have come here. I am a student of 9th. So please at least tell which subject should I refer to.

I think the resultant will be zero becoz there is equal and opposite momenta.