For a relation to be a function, each member of the domain must have a corresponding member in the range. This means that no input ( i.e. x) must have more than one output.
Therefore, to identify if a graph is a function, draw a vertical line across the graph, if the vertical line touches or intersects the graph at more than one point, it means it is not a function.
They didn't make it easy. Grid lines are apparently 3 apart, but the offered coordinates are all multiples of 4. It appears the only point that is in the doubly-shaded area is ...
