If a - b = 2 and a2 + b2 = 25, find the value of ab.  Choose the correct choice from the following options:
A) 10.5	B) 12	C) 15	D) 18	E) 20

Rationale: "explanation : 2 ab = ( a 2 + b 2 ) - ( a - b ) 2 = 25 - 4 = 21 ab = 10.5 answer : a"
Answer: A