I'm not sure how to do the problem geometrically, but if you move r red marbles and b blue marbles, there will be:

250-r red marbles and 200-b blue marbles in Container A

600+r red marbles and 150+b blue marbles in Container B

So we need 25% of the marbles in Container A to be red:

250-r = 0.25 * (250-r + 200-b)

And 75% of the marbles in Container B to be red:

600+r = 0.75 * (600+r + 150+b)

From here, you solve the two equations in the two unknowns r and b.

- Hollywood