Find the current (in A) flowing through the resistance  $R_1$ of the circuit shown in fig, If the resistances are equal to $R_1=10\Omega$ ,$R_2=20\Omega$ , $R_3=30\Omega$  and the potential of points $1,2 \& 3$   are equal to $V_1=10V,V_2=6V$  and  $V_3=5V$