For every 5 green picks, 2 are orange. Adding 5+2 makes 7. 21/7 = 3
There are 3 sets of 5 green 2 orange picks. So 2*3 = 6.
There should be 6 orange picks.
You can also just count. 5 + 2 = 7. Adding another 5 picks = 7 + 5 + 2 = 14. Another 5 picks, 14 + 5 + 2 = 21. Adding up the orange picks, which is the twos, we get 6.