Question 891633
Look at all the possible outcomes and the number of green balls. 
There are {{{2^3}}} or {{{8}}} of them.
.
.
.
GGG-3
GGR-2
GRG-2
GRR-1
RGG-2
RGR-1
RRG-1
RRR-0
.
.
.
So then for X green balls, 
{{{P(X=0)=1/8}}}
{{{P(X=1)=3/8}}}
{{{P(X=2)=3/8}}}
{{{P(X=3)=1/8}}}