In the given circuit, viewed from AB, the circuit can be reduced to an equivalent circuit as:

Thevenin's Theorem:

Thevenin’s Theorem states that “Any linear circuit containing several voltages and resistances can be replaced by just one single voltage in series with a single resistance connected across the load".

Thevenin's equivalent circuit:

Calculation of R_th:

6 Ω and 4 Ω are in parallel

\(R_{th} = {6\times 4 \over 6+4}\)

R_th = 2.4 Ω 

Calculation of Vth:

\( {V_{th} -10\over 6}+ {V_{th} -5\over 4}=0\)

\({2V_{th}-20+3V_{th}-15\over 12}=0\)

5V_th = 35

V_th = 7 V