The equation used to solve this would be 36 = g + 5g. We do this because g represents every green ballon, and since theres 5 times as many yellow as green, we can say each yellow ballon (y) would be 5 green balloons (5g).
Then we solve for g by first adding g + 5g to get 6g, then doing 36 = 6g and getting g by itself by dividing 6 from both sides.
This would get us 6 = g. That means theres 6 green balloons.