(1.1)

Thevenins theorem :

Any linear electrical network with voltage and current sources and only resistances can be replaced at terminals A-B by an equivalent voltage source V_th in series connection with an equivalent resistance R_th.

The equivalent voltabe V_th is the voltage obtained at terminals A-B of the network with terminals A-B open circuited.

(1.2)

Step 1:

Draw the circuit as 12 V battery is connected in series with a  resistor R₁.

Consider R₂ and R_L are parallel to the battery.

Using kirchoffs voltage law :

From loop I₁ :

From loop I₂ :

Multiply equation (2) with 3.

Now solve for using equations (1) and (3).

The current through load resistance R_L is 0.86 A.