The following table of numbers are the Math 160 midterm test grades of 28 students in one of Allan's classes. The test was out of 30, but there was a two mark bonus question so marks greater than 30 were possible. Note that the table has four rows of seven numbers each and the numbers are sorted in ascending order.

12 15 18 18 19 20 20 21 22 23 23 25 25 26 26 27 28 28 28 29 29 30 30 30 30 31 32 32