So sorry this is late! Hopefully this can still be useful in some way.
A: 13 students took the test. count how many dots there are, and that your answer!
B: The median score is 60. We can find this by ordering all the scores in order from least to greatest, and finding which is in the middle. In this question, its 20, 20, 20, 20, 40, 50, 60, 60, 60, 80, 80, 80, 90
C: There are 7 students that scored at least a 60. All we have to do is count how many dots there are at 60 or above!
Again, sorry for being late, but hope this helped :)