If (A-B-C+D = 13) and (A+B-C-D = 5), what is the value of (B-D)^2?  Choose the correct choice from the following answers
A) 4 . B) 8 . C) 12 . D) 16 E) 64

Rationale: a - b - c + d = 13 - - equation 1 a + b - c - d = 5 - - equation 2 adding 1 and 2 , we get 2 a - 2 c = 18 = > a - c = 9 - - equation 3 using equation 3 in 2 , we get b - d = 5 - 9 = - 4 = > ( b - d ) ^ 2 = 16 answer d
Answer: D