The line which has constant proportionality is C.
The expression which relates constant proportionality between x and y is :
Choosing a pair of points for C. ; (3, 2)
2 = 3k
k = 2/3
The expression becomes : y = 2x/3
Using the expression to determine the value of y when x = 6
y = 2(6)/3
y = 4
Also, when x = 9
y = 2(9)/3
y = 6
The values obtained also corresponds to the values of line C on the graph.