Confunsed about reactions in equilibrium

[c77793]

Hey guys, in a reaction like 1A + 1B <-> 1C + 1D, which starts with 1 mol of each molecule (A,B,C,D), how can I find out how many mols will be remaining in equilibrium state?

knowing that the Keq is equal to 4

 

[epenguin]

Write out the equation that defines K_eq. Hopefully you will see that, at least together with a very simple and elementary principle of chemistry (as well as of physics) you have all the information needed to solve the problem.