For a reaction like the example you provided, where A---> B + C, the equilibrium constant expressions would be: [B]^b[C]^c/[A]^a... where the []'s equal the concentration (mol/L) and the exponents are the coefficients used to balance the equation (so, if you added 2 to Ag in part b., the 2 would act as the exponent. Nothing in front constitutes a 1).