For a function, there will be only onle value of x. That is, a function has only one output value for each input value.
So, in the given graph, we can see that, there are
two points on x = 1, x = -3, and x = 2.
Therefore inorder to be a function, there should have only one point on x=1, 2 and -3.
Thus, three points have to be removed from the graph to make it a function.