Three children are trying to balance on a seesaw, which includes a fulcrum rock acting as a pivot at the center, and a very light board 3.2 m long. Two playmates are already on either end. Boy A has a mass of 45 {rm kg}, and boy B a mass of 35 {rm kg}. Where should girl C, whose mass is 25 {rm kg}, place herself so as to balance the seesaw?