If (64)2 - (36)2 = 20 x a, then a = ?  Choose the correct choice from the following answers.
A) 70  B) 120  C) 180  D) 140  E) 130
20 x a = (64 + 36)(64 - 36) = 100 x 28   a = (100 x 28)/20 = 140   ANSWER:140
<result>D</result>
If (64)2 - (36)2 = 20 x a, then a = ?