What the mean of 55, 899, 594, and 43648 is

Astudent received the following grades last semester. find the student's semester grade point average. an a is algebra (3 credits), a b in history ( 3 credits), a in sociology ( 3 credits) a d in english ( 3credits) and a c in seminar ( 2credits). an a is worth 4 points, a b is worth 3 points a c is worth 2 points and a d is worth 1 point.

Negative 5 1/12 + negative 4 1/4 + 6 3/4

Can someone me out here and the tell me the greatest common factor