How can you tell the substances melting point by looking at a graph?

On a graph of temperature vs. time, it shows pure substances exhibit a sharp boiling point and a sharp melting point as a horizontal flat line wherein the temperature does not change over time up until all the pure substances boiled or melted. The temperature stays stable at 160°C between 4 minutes and 11 minutes. This horizontal flat line part of the graph is normal of a pure substance. The melting point of a solid substance is usually used to specified if the substance is pure. Likewise, the boiling point of a "liquid" substance can be used to specify if the substance is pure as well.

answer; i believe that the correct answer is (light);