Solution 5:

Equating the drain currents of the MOS transistors:

Kn((Vgs - Vt,N) Vd - Vd^2/2) =

Kp((Vsg + Vt,p)Vd - Vd^2/2)

=> 80((5-1)Vo - Vo^2/2) = 80((5-1)(5-Vo) - (5-Vo)^2/2)

=> Solving the equation and finding the solution for Vo :

Vo = 2.5V