what is the probability and i only need answers for 11 through 15

For question number 11, given the following:
A bag contains:
4 green marbles
8 yellow marbles
So, the total of marbles = 4 + 8 = 12
The probability of picking a green marble the first time = 4/12 = 1/3
Then, return it again
So, the number of marble still = 12
The probability of picking a green marble second time = 4/12 = 1/3
So, the probability of both marble is green =
[tex]\frac{1}{3}\times\frac{1}{3}=\frac{1}{9}[/tex]So, the answer will be 1/9