The three elements on the left are equivalent to 2V (upper positive and lower negative) 2 ohms, and the three elements on the right are equivalent to 1V (upper positive and lower negative) 3/4 ohms.

The current on the 5 ohm resistor is (2- 1)/(2+5+3/4), and the voltage Vx=5*(2- 1)/(2+5+3/4), which is the required open circuit voltage. Input resistance R=5//(2+3/4). Norton's equivalent is =Ux/R, and the parallel resistance is R. The other two problems are calculated by this equivalent circuit, which is very simple.

The key point is to simplify the complex circuit part by part.