Selecting Applicants

Hello all.....Say there are 5 courses name A,B,C ,D and E which have vacancy 50,55,60,70 and 65 accordingly.Now  say 3000 applicants opted for these courses in different dates. Now among them  i need to select 550 applicants as per their choice and date seniority.Someone opted for course A will get it unless he is no 51th in application date seniority. What will be the SQL query?

Thanks in advance.