Consider a System of Four Gases

Consider a system of four gases. The equilibrium concentration of each product is 2.8 M. The equilibrium concentrations of the reactants are equal. The equilibrium is shown here: A + B C + D K = 2.6
What is the equilibrium concentration of gas A?

A) 3.0 M
B) 20.4 M
C) 7.3 M
D) 1.7 M
E) 0.58 M