Question

an adult and a s,all child get on a seesaw that has a movable fulcrum. when the fulcrum is in the middle, the child can't tift the adult. How should the fulcrum be moved so the two can seewaw

Answer 1

I gave you the answer. I assume, now, that you don't have numbers to plug into the equation. But you should figure out from the equation, that qualitatively, the fulcrum must be moved toward the adult.
A__________x_________C
Adult goes down. Child goes up.
So you move the fulcrum closer to the adult.
A______x______________C
Now they can see-saw.