Answer:
126 5p coins
Explanation:
Because there are three unknowns, you would need to have three equations. (1p=x, 2p=y, 3p=z). The three equations are: x+y+z=630, (2/5)*630=y, and 2z=x. Now we know that y=252. x+252+z=630, x+z=378, replace x with 2z (from last equation) to get 3z=378, so z=126.