You would multiply 20 and 35% or 0.35 since there are 20 players on the team and 35% of them play the guard position. This would equal 7 and thus your answer would be 7 players.
If the long side is 6 inches and it's 3x the length of the short side, then you need to divide the long side into 3 parts because the short side is 1/3 the length of the long side. This means that the short side is 2 inches.