Equilibrium · Equilibrium partial pressures with inert gas

One mole each of He and A(g) are taken in a 10 L closed flask and heated to 400 K to establish the following equilibrium.

$\ce{A(g) <=> B(g)}$

$K_\mathrm{C}$ for this reaction at 400 K is 4.0. The partial pressures (in atm) of He and B(g) are respectively (at equilibrium).

(Assume He, A(g) and B(g) behave as ideal gases)

(Given : $R = 0.082$ L atm K$^{-1}$ mol$^{-1}$)