With this! i need to discern whether or not they represent a function.

A function associates a value from a set (domain) one and only one value from another set. IE, from the same x value you can have only one y. So pick a ruler and scan each graph parallel to the Y axis. If you touch the blue line in two points, that's not a function.

Since 7 and 11 are both rational, the sum and difference are rational.