Find the current throught the load using Thevenin's theorem. The load is connected across the points a and b. Short the load resistance and find the voltage across a and b. This is the thevenin voltage. Find the resistance as seen from the points a and b. This is thevenin resistance. Replace the circuit by the Thevenin circuit. Across the points a and b connect the load resistor and find the current through it. Verrify with the original circuit and see it will be same.