Finding Vds in a CMOS without info. on channel modulation?
The OP provided a sample solution to the problem as,



Turning to spice, we can determine the complete hypothetical solution as,



Spice estimates the output to be,
$$ Vo \simeq -50 \textrm{ mV} $$

The practical aside is if M4 is 1% larger than expected, the input offset voltage causes the output to rail.