urgent Lever Question ( i want to learn how to do it)

Question

Timmy and Janie sit on opposite ends of a 20-foot-teeter-totter. Timmy weighs 60 pounds and Janie weighs 40 pounds. Where would Sally, who weighs 50 pounds, have to sit to balance the teeter-totter? (The fulcrum is at the center.)

Answer 1

As shown in the diagram, Sally should sit to Janie side because Janie weighs less than Timmy

=> 40lb(10ft) + 50lb(X) = 60lb(10ft)

=> 50lb(X) = 60lb(10ft) - 40lb(10ft) = 200lb-ft

=> X = 200lb.ft/50lb = 4ft

Hence Sally should sit 6ft away from Janie