V0 will be either at+Vsat or Vsat
Voltage V1 at node 1,
V1=2V0+4V16=V03+23Vi
As, V1=0
Then V0=−2Vi
Vi=−V02
So for V0=+Vsat
Vi=VTL=−122=−6V
and for V0=−Vsat
V0=VTH=122=6V
∴VTH−VTL=6−(−6)=12 V