A uniform plank of length 6.0 m and weight 231 N rests horizontally on two supports, with 1.1 m of the plank hanging over the right support (see the drawing). To what distance x can a person who weighs 451 N walk on the overhanging part of the plank before it just begins to tip?

Answer 1

You have two equations you can write.
1) Sum forces vertical=0
LS + RS-231-451=0 where LS, Rs are the forces on the right support.
2) You can sum moments about any point. Hmmm. YOu didn't say where the left support is.
Anyway, sum momemts about the left support (RS, cg, man) and set to zero.
Then sum moments about the RS.

That ought to give you sufficent equations to solve.