Let's list out the information given
Total marble = 12
The bag contains white, red, green and yellow marbles
P(white) + P(yellow) = P(green)
P(green) + P(red) = 1
P(white) = 10/40 = 1/4
If 2 green marbles are removed from the bag,we have 10 marbles left
P(red) = 1 - P(green): 1/5 = 1 - P(green)
P(green) = 1 - 1/5 = 4/5
P(green) after removing the 2 marbles = (4/5) = 8 green marbles out of 10 total marbles
P(green) before removing the 2 marbles = (8+2)/(10+2) = 10/12 = 5/6
P(white) = 1/4 * 12 = 3 marbles
P(white) = 3 marbles