a 70kg person want to seat on a seesaw which has a length of 4 m, how far would they need to be from the pivot in order to rock back and forth easily?...

If a 40 kg person and a 70kg person want to seat on a seesaw which has a length of 4 m, how far would they need to be from the pivot in order to rock back and forth easily? (the pivot point is on the middle of the seesaw) Show your work.