If (A-B-C+D = 13) and (A+B-C-D = 9), what is the value of (B-D)^2? Pick one
A) 4 .
B) 8 .
C) 12 .
D) 16 .
E) 64 .

Rationale: "eq 1 : a - b - c + d = 13 eq 2 : a + b - c - d = 9 ( 1 ) subtract eq 1 from eq 2 a - b - c + d = 13 - a + b - c - d = 9 - - - - - - - - - - - - - - - - - - - - - - - - - 2 b + 2 d = 4 ( 2 ) simplify - b + d = 2 b - d = - 2 ( b - d ) ^ 2 = ( - 2 ) ^ 2 = 4 my answer : a"
Answer: A