Imani would like to approximate the number of students in her school with part time jobs. She surveys the 28 students in her math class. Is this baised or unbaised?

Biased, because there is only survey of one group of people (one grade, one class). The sample (the class) is too small compared to the population (assuming it's an average school size). You will end up with less than 1 percent of the population size thus the survey is not reliable information.