Answer:S3 = 39 Step-by-step explanation:* an = 3(3)^(n-1) is a geometric sequence* The general rule of the geometric sequence is: an = a(r)^(n-1)Where:a is the first termr is the common difference between each consecutive termsn is the position of the term in the sequenceThe rules means:- a1 = a , a2 = ar , a3 = ar² , a4 = ar³ , ........................∵ an = 3(3)^(n-1)∴ a = 3 and r = 3∴ a1 = 3∴ a2 = 3(3) = 9∴ a3 = 3(3)² = 27* S3 = a1 + a2 + a3∴ S3 = 3 + 9 + 27 = 39 Note: We can use the rule of the sum:Sn = a(1 - r^n)/(1 - r)S3 = 3(1 - 3³)/1 - 3 = 3(1 - 27)/-2 = 3(-26)/-2 =3(13) = 39