A reminder to read the contest rules (http://checkmateupdate.blogspot.com/2010/11/countdown-begins-soon.html) before attempting to send your answers :)
Countdown #4 - Piece Scales
Value: 2 points
In a non-standard chess game, there are three types of pieces - pawns, knights and rooks. They have non-standard values which cause them to be in balance in the first two situations (scales). How many rooks are needed to replace the question mark to balance the third scale?