The following data shows the marks obtained by students in a class. 39 30 5 65 5 21 5 65 89 30 91 30 64 64 91 15 89 48 30 64 85 30 69 51 32 85 48 91 30 28 68 48 65 30 65 35 65 48 48 15 91 30 91 48 71 15 65 48 71 38 Find the mode of the class marks of the students.