A person lies on a platform which has a scale under both ends. imagine the scale on the left reads 575 n and the scale on the right reads 280 n. when the person gets off the platform, both scales read 70.0 n.

Let us say that the platform is L long and the person is x from the left hand end.

And so taking the moments about the left hand end:

(575 + 280 - 140) (x) + 140 (L/2) = 280 (L)

715 x = 210 L

x = 0.294 L

So the center of mass of the person is located 0.294L from the left.