If a - b = 3 and a(power 2) + b(power 2) = 21, find the value of ab.
Choose the correct choice from the following answers: A) 5 B) 8 C) 4 D) 6 E) 3
2ab = (a(power 2) + b(power 2) - (a - b)(power 2)   = 21 - 9= 
<gadget id="calculator">21 - 9</gadget>
<output>12</output>
12   ab= 6.   Answer is 6.
<result>D</result>
If a - b = 3 and a(power 2) + b(power 2) = 21, find the value of ab.