Let S_{n} be the sum of the first n term of an arithmetic sequence that has a common difference of 2 . The quotient \dfrac{S_{3 n}}{S_{n}} does not depend on n. What is S_{20} ?

**Answer Choices**

A. 340

B. 360

C. 380

D. 400

E. 420

Let S_{n} be the sum of the first n term of an arithmetic sequence that has a common difference of 2 . The quotient \dfrac{S_{3 n}}{S_{n}} does not depend on n. What is S_{20} ?

**Answer Choices**

A. 340

B. 360

C. 380

D. 400

E. 420