.
After 1-st transfer,
    With the probability  
 = 
  you will get (7+1 blue, 3 green) = (8 blue,3 green) in the bag   
    (call it "case A". It is the case when a blue jelly was transferred);
    with the probability  
 = 
  you will get (7 blue, 3+1 green) = (7 blue,4 green) in the bag   
    (call it "case B". It is the case when a green jelly was transferred).
After the selection from the bag, 
    the probability to get a green jelly from the bag is  
 = 
  in case A,  and
    the probability to get a green jelly from the bag is  
 = 
  in case B.
Thus the probability to get a green jelly from the bag is 
    P(green) = 
 + 
 = 
 +  
 = 
 = 
.
Now use the formula for conditional probability to get the answer to the problem's question
    P(green at the first transfer) = 
 = 
 = 
 = 
 = 
.    ANSWER
Completed and solved.