In order to find the constant of proportionality between x and y, you consider the following equation:
y = rx
where r is the constant of proportionality. First, you solve for r in the previous equation:
r = y/x
To calculate r, you can use any of the given point (x,y) in the table. That is, if you choose x = 2 you have to choose y = 14 too.
You replace x and y and you obtain:
r = 14/2
r = 7
Hence, the constant of propotionality is 7
