hafta do a project for class, not too good with statistics...

the step im on is...
3. It is desired that the data be divided into 4 groups (each group corresponds to a
grade A, B,C or D)
o Lets assume that the number of members in each group are same. Identify
the cut-off for the 4 groups.
o Assume that students below 25th percentile are to be assigned a grade D.
Identify the cut off.

there are 80 students in the study (a list of midterm grades) so that would be 20 in each group. im not exactly sure what they are looking for with the bullet point questions, any help would be appreciated