Solution
For this problem we need to remember that the constant of proportionality is given by:
k= y/x
And if we select the last point of the graph we can see that x= 6, y= 15 and replacing we got:
k= 15/6
The greatest common factor between 15 and 6 is GCF=3
15/3= 5
6/3=2
And then our answer is 5/2 simplified
And our solution for this case would be 5/2=2.5