in cases of gas, it's called Kp , not Kc, because you use partial pressure instead of concentration to calculate the equilibrium constant.

your ICE table is right, but not your calculation. let x be the partial pressure of B.

partial pressure of A at eqbm = 5 - 2x = 3.5atm

2x = 5 - 3.5 = 1.5atm

x = 0.75atm

partial pressure of B = x = 0.75atm

partial pressure of C = 3x = 2.25atm

Kp = (C^{3}*B)/A^{2} = (2.25^{3}*0.75)/3.5^{2} = 0.6973 ~ 0.70atm