Constant of proportionality is the constant value of the ratio of two proportional quantities x and y; usually written y = kx, where k is the factor of proportionality.
To make color pink,
for every 3 cups of red , we need 7 cups of white.
Let 'r' be the cups of red required
let 'w' be the cups of white required
so , as per the question
for 3 r we need = 7 w
r = 7/3 w
so, 7/3 is constant of proportionality
