Calculate the Thévenin Voltage (Vt) and Thévenin Resistance (Rt) equivalent of the circuit below
Do it the same way you always would:


Calculate the open circuit voltage. With no load connected between A and B, what will be the voltage \$V_{AB}\$? That is the Thevenin voltage \$V_{th}\$.
Calculate the short circuit current. If A and B were shorted, what current would flow through that short? If the short circuit current is \$I_s\$ then the Thevenin resistance is \$R_{th}=V_{th}/I_s\$.


If it helps you to visualize the problem, then you can re-draw the circuit however you like, provided you maintain the same connections between the elements.