The average of thirteen numbers is 47. The average of the first three numbers is 39 and that of next seven numbers is 49. The 11^th number is two times the 12^th number and 12^th number is 3 less than the 13^th number. What is the average of 11^th and 13^th numbers?

A. 56.5

B. 56

C. 54.5

D. 57

Answer: Option D