If both mass and speed are doubled, what happens to its momentum?

The general formula is:      Momentum = (mass) x (speed)

I never like to just write a bunch of algebra without explaining it.
But in this particular case, there's really not much to say, and
I think the algebra will pretty well explain itself.  I hope so:

Original momentum = (original mass) x (original speed)

New momentum = (2 x original mass) x (2 x original speed)

                           = (2) x (original mass) x (2) x (original speed)

                           = (2) x (2) x (original mass) x (original speed)

                           =  (4) x (original mass) x (original speed)

                           =  (4) x (original momentum).