Yes. M+3=-5, subtract 3 from both sides: -5-3=-2: m=-2. M=-2 is the same as m=-2 :)
You would have to calculate the percent first.
Add the total number of students
3420+4680= 8100 students TOTAL
Then you would divide the amount of students by the total
3420 part time/8100 students total = .42 or 42%
4680 full time/8100 total = .58 or 58%
Then you multiply the percentages by 90
(90)(.58)= 52.2
(90)(.42)= 37.8
Rounded
52 full time and 38 part time students