Carbon tetrachloride can be produced by rollowing reaction:

CS2(g) + 3 Cl2 (g) --> S2Cl2(g) + CCl4 (g)

suppose 1.2 mol of CS2 and 3.6 mol of CL2 are placed in a 1.00-L flask. After equilibrium has been achieved, the mixture contains 0.90 mol of CCl4. Calculate K.

How do you go about solving this?