y ∝ x
y = kx
where k is the constant of proportionality
we need to find the value of k
substitute x=12 and y=9.6 into the equation above and solve for k
9.6 = k(12)
Divide both-side by 12
k=0.8
This implies that;
y = 0.8x
when x=20, then the value of y is:
y=0.8(20) = 16
Therefore, when x=20 y=16