Can someone explain to me why they carry over a voltage (2<0 V) in the third circuit. Also why is it 2 and how did they get it?. I am also confused on why the resistor is 4 instead of 1 in the third image.

 

Hi,

Short answer is that you can reflect values on the secondary to the primary to help solve these circuits.
For example, resistance reflects as the square of the turns ratio.

 

Thank you. I figured it out through your explanation.