Applying KCL at mesh 2, we get

-2 i_2-3\left(i_2-i_3\right)-1\left(i_2-i_1\right)=0         (i)

The combined mesh equations for meshes (1) and (3) are

\text { (7) }\left(i_1-i_2\right)-3\left(i_3-i_2\right)-1 . i_3=0        (ii)

Solving, we get i_3=2 A , i_1=9 A , i_2=2.5 A

Inside the super mesh, applying KCL, we get

i_1=7+i_3-7-i_3+i_1=0

i_1-i_3=7             (iii)

So, the power dissipation is

P=\left(i_2-i_3\right)^2 \times 3=(0.5)^2 \cdot 3 \Rightarrow P=0.75  W

Note: Since the voltage across an ideal current source can be of any value, it is not possible to write the mesh equations for the meshes (1) and (2) independently.
Hence, the supemesh procedure is followed.