This is because she gave a random sample, but the she had the convenience of the students being with her when she surveyed. So it'e not actually random. She could also worded the survey or gave a biased response.
A dot above 7, 4, 10, 2, and 20. Draw a box around the median, first quartile, and and the third quartile. Then connect the box to the minimum and maximum by drawing a line. Should look like this:
