As I (we?) near the completion of the Da Vinci Code game, I finally got an answer to the "exarad" question. Joanna (who I don't know, but it's hot that a random woman answered this question for me) writes:
Nope, you're right! Bob is a tad off. [Editor's Note: Bob's always been "a tad off". Just kidding, Bob :)] The answer works out to be c^2 (c = light speed = 299,792,458 m/s, obviously). But they want it in exarads! Eep! Rads don't refer to radians here, but radiation (http://en.wikipedia.org/wiki/Rad_%28unit%29), which is expressed in J/kg (joules per kilogram), which can be converted to m^2/s^2 (http://www.vsg.cape.com/~pbaum/si.htm). So by rounding up to the nearest whole number you get an answer of 9. This game was made for geeks like us! :P
Only two more days until the game is complete. I hope one of us wins the Cryptex.