At 25°C, the Equilibrium Constant K_c for the Reaction 2A(g)

At 25°C, the equilibrium constant K_c for the reaction 2A(g) ⇄ B(g) + C(g)
Is 0.035. A mixture of 8.00 moles of B and 12.00 moles of C in a 20.0 L container is allowed to come to equilibrium. What is the equilibrium concentration of A?

A) < 0.100 M
B) 0.339 M
C) 0.678 M
D) 6.78 M
E) 13.56 M