[UPSC IFoS 2014] Electrostatics and Magnetostatics (Q127, 10M)

Explain Kirchoff's circuit laws. Using Kirchoff's laws find currents $I_1$ , $I_2$ and $I_3$ in the circuit shown below for $R_1 = 100\ \Omega$ , $R_2 = 200\ \Omega$ , $R_3 = 300\ \Omega$ , $E_1 = 3\text{ V}$ , $E_2 = 4\text{ V}$ .