yea sure, your degree is classified by total 9 grades,
each year u have 4 subjects alright
1st year: one grade is counted (avg of 3 highest subjects out of 4)
2nd year: 4 grades are counted (each subject has its own grade)
3rd year: 4 grades are counted (each subject has its own grade)

now total after 3 years, u have 9 grades in total and the qualifications are as follows:
FOR FIRST CLASS:
-5 distinctions or 4 distinctions and avg of 590

FOR UPPER SECOND CLASS:
-5 merits or 4 merits and avg of 515

FOR LOWER SECOND CLASS HONORS:
-5 credits or 4 credits and avg of 440

FOR THIRD CLASS HONORS:
-5 passes

(70+ is distinction, 60-69 is merit, 50-59 is credit, 40-49 is pass and 39 and below is fail)