Solve this question in functions which seems to be diifficult?

the question is
if g(x) is a polynomial satisfying

g(x)g(y)=g(x)+g(y)+g(xy) - 2

for all real x and y, and g(2)=5
then find g(3).

the answer is 10
please tell me how to do this ques.

My sir told me that this ques. could be solved in a quarter of page.
But any advice is appreciated
thanks