We can solve this problem in two ways.
1. From the description we conclude that the described sequence is a geometric sequence where the first term a₁ = 2 and common ratio r = 3, so:
Answer D.
2. The easiest way. We know that a₁ = 2, so let's substitute n = 1 for each of the possible answers:
A. 3·2ⁿ = 3·2¹ = 3·2 = 6 - Wrong
B. 2·3ⁿ = 2·3¹ = 2·3 = 6 - Wrong
C. 3·2ⁿ⁻¹ = 3·2¹⁻¹ = 3·2⁰ = 3·1 = 3 - Wrong
D. 2·3ⁿ⁻¹ = 2·3¹⁻¹ = 2·3⁰ = 2·1 = 2 - Correct.