(b) Applying Kirchhoff’s law for the loops (1) and (2) as shown in figure
For loop (1)
$- 2i_{1} - 2\left( i_{1} - i_{2} \right) + 4 = 0$
$\Rightarrow 2i_{1} - i_{2} = 2$ …(i)
For loop (2)
$- 2\left( i_{1} - i_{2} \right) + 4i_{2} - 6 = 0$
$\Rightarrow - i_{1} + 3i_{2} = 3$ …(ii)
On solving equation (i) and (ii), $i_{1} = 1.8A$