Now consider the reaction a+2b⇌c for which in the initial mixture qc=[c][a][b]2=387 is the reaction at equilibrium? if not, in which direction will it proceed to reach equilibrium? now consider the reaction

Solving this chemistry is a little bit hard because the question didn't give some important detailed. 
So first, there are a couple problems with your question. 
We will just need to know which direction will it proceed to reach equilibrium.
Your expression for Kc (and Qc ) for the reaction should be: 
Kc = [C] / [A] [B]^2 
You have not provided a value for Kc, so a value of Qc tells you absolutely nothing. Qc is only valuable in relation to a numerical value for Kc. If Qc = Kc, then the reaction is at equilibrium. If Q < K, the reaction will form more products to reach equilibrium, and if Q > Kc, the reaction will form more reactants.

Temperature and pressure