By equation of equilibrium and friction:
Fb = Kx = 15(0.175) = 2.625 kN.
The wedge is on the verge of moving right then slipping will have to occur at both contact surfaces.
Fa = usNa = 0.35Na
Fb = 0.35Nb
Nb = 2.625 = 0; Nb = 2.625 kN
Nacos10 – 0.35Na sin 10 = 2.625 = 0
Na = 2.841 kN
P – (0.35 * 2.625) – 0.35 (2.841) cos 10 – 2.841 sin 10 = 0
P = 2.39 kN