To be balanced, weight x length has to be equal on both sides. Let X be the unknown distance. X/9 = 25/75 Multiply by 9 to isolate X then do math on right side. That is one distance. Subtract that from 9. That is the other distance. Where should the pivot be from the adult? Multiply X x 75. Does that = (9 - X) x 25? If it does then that is where the pivot should go.