If a - b = 3 and a^2 + b^2 = 28, find the value of ab.	Choose the correct choice from the following choices:
A) 19  B) 15  C) 10  D) 8  E) 13
2ab = (a^2 + b^2) - (a - b)^2   = 25 - 9= 
<gadget id="calculator">25 - 9</gadget>
<output>16</output>
16   ab= 8.   Answer is 8.
<result>D</result>
If a - b = 3 and a^2 + b^2 = 28, find the value of ab.