marbles mystery

Ramesh has five boxes containing 4, 8, 9, 12 and 100 red and blue marbles. One box contains only red marbles; another contains only blue marbles; while the other three contain both red and blue marbles. When his younger brother Rakesh took a box, Ramesh exclaimed “Now, I have an equal number of red and blue marbles!” Which box did Rakesh take?