Homework Help

I'm having trouble with question 1b on http://www.physics.drexel.edu/students/courses/physics-201/assign/Phys201AssignH2F08.pdf
I've tried setting y=0 at the very top(equilibrium with no mass) and at the middle(equilibrium with a mass).  My math just isn't working out, I've gotten as close as.
I've gotten as far as this;
the difference between equilibrium and top;
KYoYm-(1/2)K(Ym)^2-MGYo-MGYm
and the difference between equillibrium and bottom;
-KYoYm-(1/2)K(Ym)^2-MGYo-MGYm

>The spring stretches by "yo" under the load and comes to equilibrium position

y=0 @ bottom of unstretched spring

OP here;
setting Y=0 at the end of an unmassed spring wont let you have the sums of potential energy due to elastic and potential energy due to gravity from the top and bottom of it's oscillations equal out, so I set it to the equilibrium position with a mass, so the potential energy due to gravity opposes itself on either side