A board game comes with 9 white and green number cubes and there are twice as many white cubes as green cubes How many cubes of each color are there?

There are 6 white cubes and 3 green cubes.

Algebraically, the equations are W = white cubes, G= green cubes

W+G = 9 and W = 2G so substituting we have 2G + G = 9, and 3G = 9, so G=3 and W=6.