Answer:
3/16 or 3:16 (whatever form works for you)
Step-by-step explanation:
The ratio is the number of green marbles over the total number of marbles. 
There are 3 green marbles so our numerator is 3. 
There are 3 + 2 + 4 + 6 + 1 = 16 marbles in total. 
This makes it 3/16
P.s. Is this actually an AP. exam and if it is then which one??