If a - b = 3 and a^2 + b^2 = 27, find the value of ab. Select:  A) 12  B) 15  C) 10  D) 18  E) 9

Rationale: "2 ab = ( a ^ 2 + b ^ 2 ) - ( a - b ) ^ 2 = 27 - 9 = 18 ab = 9 . answer is e ."
Answer: E