Plug in numbers in for x.
If you plug in 0 then you get 1. 1/0 is undefined
If you plug in 1 then you get 6. 6/1 is 6
If you plug in 2 then you get 11. 11/2 is 5.5
If you plug in 3 then you get 16. 16/3 is 5.3 repeating
If you plug in 4 then you get 21. 21/4 is 5.25
If you plug in 5 then you get 26. 26/5 is 5.2
It would only be proportional if you got the same answer after dividing each time.