I don't understand please helpp

When you answer this can you explain

:24% of students in a class are girls. if there are less than 30 students in this class, how many students are there? how many girls are there?

This is a map of the mars exploration rover opportunity predicted landing site on mars. the scale is 1cm : 9.4km. what are the approximate measures of the actual length and width of the ellipse? i mostly need to know how to set it up : )