I have a ggplot graph that has several functions graphed on it. I would like to smooth each line using a three point moving average. How can I go about going through that?
This is my image: 
This is some of my data:
YEAR Topic Perct
1981 A 40
1981 B 12
1981 C 12
1982 A 38
1982 B 8
1982 C 14
1983 A 39
1983 B 13
1983 C 18
1984 A 40
1984 B 11
1984 C 13
1985 A 42
1985 B 9
1985 C 15
1986 A 44
1986 B 11
1986 C 14
1987 A 42
1987 B 13
1987 C 18
1988 A 40
1988 B 12
1988 C 18
1989 A 42
1989 B 11
1989 C 19
1990 A 39
1990 B 10
1990 C 18
