If a - b = 3 and a(power 2) + b(power 2) = 21, find the value of ab.
Choose the correct option
A) 5
B) 8
C) 4
D) 6
E) 3

Rationale: "2 ab = ( a ( power 2 ) + b ( power 2 ) - ( a - b ) ( power 2 ) = 21 - 9 = 12 ab = 6 . answer is d ."
Answer: D