Answer: The graph is a function
It is a function because we do not have two or more red points vertically aligned. In other words, we don't have any red points stacked. This graph passes the vertical line test.
The vertical line test is where we try to find a single vertical line passing through more than one red point. No such vertical line exists, so that's why this graph passes. Passing the vertical line test means we therefore have a function.
A function is where any input x leads to exactly one output. For instance, the input x = 9 leads to the single output y = 28. Similar situations happen with the other x values as well. If we had the two points (9,28) and (9,36), then this wouldn't be a function.