Answer:
We have been given an equation 
We will factorize it by middle term splitting.
Step 1: 
Taking common factors out by clubing first two terms ad last two terms
Step 2: 
Step 3: 
Equating both above factors to zero as:
Step 4: 
And
.
The answer is 8...............
3 marbles as there is only one green and there is three other blue marbles left and that answer is incorrect