A relationship is proportional if the ratio between the output and the input is constant:
[tex] y=kx \iff \dfrac{y}{x} = k [/tex]
In your case, we have
[tex] \dfrac{65}{1} = \dfrac{130}{2} = \dfrac{195}{3} = \dfrac{260}{4} = \dfrac{325}{5} = \dfrac{650}{10} = 65 [/tex]
This means that it takes the reader one unit of time to read 65 pages. So, after 2 units of time, he reads 130 pages, and so on.
