Everything that is given in ordered pairs is a relation. But not all relation is a fuction. In this case it is, because there is no repeated information. For example. If in 1 week he reads 20 books and in the same week he reads 30 books, there is information repeated, so that would not be a function. If you wanted to see it like ordered pairs, you can not have somethin like this in a fuction
Because you will have a domain point with two different images.