In this case, we'll have to carry out several steps to find the solution. 
Step 01:
Data
Table 
proportional relationship = ?
Step 02:
relationship: 
y = k x 
k = y / x 
c = y 
n = x 
k1 = 120 / 72 = 1.667...
k2 = 135 / 81 = 1.667...
k3 = 150 / 87 = 1.724
k4 = 160 / 104 = 1.538
k1 = k2 ≠ k3 ≠ k4 
The constant of proportionality is not constant. 
The answer is: 
The relationship is not proportional