If (A-B-C+D = 18) and (A+B-C-D = 6), 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) 36 .

Rationale: "eq 1 : a - b - c + d = 18 eq 2 : a + b - c - d = 6 ( 1 ) subtract eq 1 from eq 2 a - b - c + d = 18 - a + b - c - d = 6 - - - - - - - - - - - - - - - - - - - - - - - - - 2 b + 2 d = 12 ( 2 ) simplify - b + d = 6 b - d = - 6 ( b - d ) ^ 2 = ( - 6 ) ^ 2 = 36 my answer : e"
Answer: E