4+3+3 = 10 total marbles
4 are green so 4/10, reduced to 2/5 of picking a green one first.
without replacing it, there would be 9 marbles and 3 green ( assuming he picked a green one first)
so 3/9 reduced to 1/3 that the 2nd one would be green
2/5 x 1/3 = 2/15 probability of picking 2 green marbles