Question

You have 15 blue marbles. Your friend Duong takes away 3 and gives you 2. You drop 8 but pick up 4. Hung takes 4 and gives 5. You take one from Duong and give it to Hung in exchange for 3 more. You give those 3 to Duong and she gives you a blue and a yellow. Phong comes and takes the blue marbles Duong gave you and gives you a green. You give the green to Hung in exchange for a blue marble. Phong then takes a blue marble from Duong, gives it to Hung for a yellow, and gives you the yellow for a blue marble. How many green marbles do you have?