Physics Problem..Rotational Equilibrium..Help Please..?

[Hot Guy]

1) A 15-kg child and a 25-kg child sit at opposite ends of 4.0m
seesaw pivoted at its center. Where should a third child whose mass is 20kg sit in order to balance the seesaw?

2)A man is doing push-ups. He has a mass of 68kg and his center of gravity at a horizontal distance .70m from his palms and 1m from his feet. Find the force exerted by the floor on his palms and feet.

3) A person places his palm and pushes downward a scale until it reads 96N. The triceps muscle is responsible for this arm extensive force. Find the force exerted by the triceps muscle. The bottom of the triceps muscle is 2.5cm to the left of the elbow joint and the palm is pushing approx. 38cm to the right of the elbow joint..

Thank you very much to those who'll be helping me.. ^_^
Pls. explain the steps u did to find the final answer...