Measurement were made on a two port network shown in figure

a) with port 2 open, a voltage of 100 ∠0 volt is applied to port 1 that resulted in I₁ = 10∠0 amp V_2­ =25∠0 volts.

b) With port 1 open, a voltage of 100∠0 volts is applied to port 2 that resulted in I₂ = 20∠0 amp and V₁ = 50∠0 volts.

The value of Z₁₁ Z₂₂ – Z₂₁ Z₂₂ is