Method for getting correct answer? Thank you!

Initially there were equilibrium concentrations of 0.1887 M A, 0.1042 M B. Which of the equations below is correct if the pressure decreased by a factor of 2.40? Use the reaction below.
6A(g) ↔ 5 B(g)

a. Qc = 0.42 Kc

b. Qc = 0.45 Kc

c. Qc = 2.40 Kc

d. Qc = 0.38 Kc

I just posted a response at the original site below.