Explanation:
the constant k of proportionality is defined by
y = kx
or in our case
b = ka
so, let's see
14 = k×2
k = 14/2 = 7
this also works for the other data pairs :
7×5 = 35
7×9 = 63
7 × 1/3 = 7/3
perfect.
so, the constant of proportionality is 7.