Find the First and Third Partial Sums, S1 and S3 $$a _ { n } = 3 n + 9$$

Multiple Choice

Find the first and third partial sums, s1 and s3, for the sequence
- $$a _ { n } = 3 n + 9$$

A) 12, 45
B) 12, 18
C) 12, 36
D) 12, 42