HELP!!!!!!!!!!!!!!!!

Year Number of Dropouts
1 7
2 8
3 6
4 6
5 6
6 4
7 4
8 1
9 2
10 7
11 6
12 1
13 1
14 1
15 3
16 3
17 5
18 4
19 5
20 7
The table gives 20 years of data on the number of students in a particular school who dropped out in the ninth grade. A sample is taken to include only the last 3 years of this data. With this information, calculate both the population mean and the sample mean for ninth-grade dropouts per year.

Question

HELP!!!!!!!!!!!!!!!! 

Year	Number of Dropouts
1	7
2	8
3	6
4	6
5	6
6	4
7	4
8	1
9	2
10	7
11	6
12	1
13	1
14	1
15	3
16	3
17	5
18	4
19	5
20	7
The table gives 20 years of data on the number of students in a particular school who dropped out in the ninth grade. A sample is taken to include only the last 3 years of this data. With this information, calculate both the population mean and the sample mean for ninth-grade dropouts per year.