Sumif/s maybe! + percentage

May be like this:
on cell B5

=SUMPRODUCT(COUNTIFS(Table1[End of Year 1 Target],'Class Information'!A2:A12,Table1[Mark],{"1a","2a","2b","2c"}))/B4

on cell b6

=(B4-SUMPRODUCT(COUNTIFS(Table1[End of Year 1 Target],'Class Information'!A2:A12,Table1[Mark],{"1a","2a","2b","2c"})))/31

Note:
- as EleGault mention, change your cell format into percentage

- on cell b6 you can use EleGault formula too