In an arithmetic sequence, the 3rd term is 7 and the 7th term is 19. What is the 15th term of the sequence?

✓ Correct Answer: Option A

Let `a_n = a_1 + (n-1)d`. `a_7 - a_3 = 4d = 19 - 7 = 12`, so `d=3`. `a_3 = a_1 + 2d = 7` => `a_1 + 2(3) = 7` => `a_1 = 1`. Then `a_15 = a_1 + 14d = 1 + 14(3) = 1 + 42 = 43`.