To explain for melting point, left image shows substance x being a solid at 25 degrees. So the plausible options should be above 25 degrees as melting point.

For boiling point, since image on right shows flowable liquid form of substance x. Hence, to deduce state of matter at the temperature stated in caption would be liquid form instead of the boiling point. Boiling point would mean that substance x is in vapour or gaseous state, not exactly visible to the human eye. Hence, boiling point should be greater than the stated temperature in caption. And since option 3 satisfy both criteria for melting and boiling point temperatures, the answer is 3