The mass m is in equilibrium so the value of tension will be mg.
In mass 2m six forces are acting
1. T = mg at bottom in horizontal direction
2. Its weight in downward direction 2mg
3. Normal reaction from the surface in upward direction N
4. The upper pulley attached applies force of tension T in horizontal direction away from the mass and a force equal to T in downward direction.
Balance the vertical forces ,
N = T +2mg = 3mg
5. The frictional force equal to uN = u3mg
Balance the horizontal force ,
T+T= friction
mg +mg = 3mgu
u = 2/3
Hope you understood.
