find the value of $\displaystyle I_1,I_2,I_3$
Let $\displaystyle i_1$ be the current from E1 towards R1
and $\displaystyle i_2$ be the current from E2 towards R2
-----
Use Kirchhoff's loop law
We get
For the loop of potential E1
$\displaystyle 6 = 3i_1 + 4(i_1 + i_2) $
For loop of E2
$\displaystyle 12 = 12i_2 + 4(i_1 + i_2) $
--------
two equations and two unknowns....
$\displaystyle i_3 = i_1 + i_2 $
--------
I hope this one is clear than the one I told you there... :-)