Suppose a child is sitting 5 feet from the fulcrum. Where does a 175 pound adult need to sit for the seesaw to be balance?

Answer 1

It's a levers problem.
So You need to know following.

Weight1 *Distance1(from fulcrum)=W2 *D2

What is child's weight? If 70 lb,
70 *5 =175 * X

So X=2
Adult need to sit 2 feet from the fulcrum.