What is the primary purpose of applying the vertical-line test to a graph?

To find the y-intercepts of the graph.

To determine if the graph represents a function.

To check if a function is a one-to-one function.

To calculate the area under the curve.

A graph contains the points $(4, 9)$ and $(4, -2)$. What can be concluded about this graph?

The graph passes the vertical-line test.

The graph fails the vertical-line test.

The graph has an x-intercept at 4.