I can only solve this using Kirchhoff Laws and Ohm's Law.
The first thing i tried was finding the current through R3 , Ir3=1mA (Ir3 = 12/12.10^3 = 1mA).
Then using KCL on node A: Ir2 = Ir3 + Ir1 <=> 2 = 1 + Ir1 <=> Ir1 = 1mA.
And finally using KVL to find Vs : -Vs+R1*Ir1+R2*(Ir1-Ir3)=0<=>-Vs+6+6(1-1)=0<=>-Vs =-6<=> Vs=6.(Which is wrong)
But i can't get the correct answer, i suspect im doing wrong the KVL and i've been trying for the last hour different things . Appreciate any help...(I know the correct answer ,which is 24V, in my question i expected someone to point where in my logic it went wrong to get a different answer)