Rosana is tracking how many customers she can serve in a morning. she listed the number of customers served per hour in the following table:

hour (x) number of customers
f(x)
1 3
2 5
3 7

determine if these data represent a linear function or an exponential function, and give the common difference or ratio.

Set $r$ is a set of rectangles such that (1) only the grid points shown here are used as vertices, (2) all sides are vertical or horizontal and (3) no two rectangles in the set are congruent. if $r$ contains the maximum possible number of rectangles given these conditions, what fraction of the rectangles in set $r$ are squares? express your answer as a common fraction.