Physics
posted by Kyla .
Three children are trying to balance on a seesaw, which consists of a fulcrum rock, acting as a pivot at the center, and a very light board 6.0 long . Two playmates are already on either end. Boy A has a mass of 50 , and girl B a mass of 35 . Where should girl C, whose mass is 25 , place herself so as to balance the seesaw?

I would sum moments about the center fulcrum.
clockwise moments are +
50*3+25x+35*3=0
solve for x, the distance from the center to the Cgirl measured toward the GirlB. 
1.8