kg
b =  ← blue varies directly to greens and inversely as whites squared
w²
k(3)
4 = 
2²
3k
4 = 
4
3k = 16
k = 16/3 ← constant of variation
kg
b = 
w²
(16/3)g
2 = 
4²
(16/3)g
2 = 
16
32 = (16/3)g
g = 6
6 green
 Proof
