For the circuit shown in figure, determine the voltage across $4\mathrm{\Omega }$ resistors in volt ?

Flow the current in the circuit as shown in figure. 

Writing KVL equation for loops, I, II and III

$-9+3\mathrm{I}+6{\mathrm{I}}_1=0,4{\mathrm{I}}_2+2{\mathrm{I}}_3+{\mathrm{I}}_2-6{\mathrm{I}}_1=0$

$2{\mathrm{I}}_4+4-2{\mathrm{I}}_3=0$

Using KCL ; $\mathrm{I}={\mathrm{I}}_1+{\mathrm{I}}_2\Rightarrow {\mathrm{I}}_2={\mathrm{I}}_3+{\mathrm{I}}_4$

Solving above equation we get ${\mathrm{I}}_2=0.5\mathrm{A}$

So, potential difference across $4\mathrm{\Omega }$ resistor is, $\mathrm{V}=4{\mathrm{I}}_2=4\times 0.5=2\text{ volt }$