In this question, we aren't given the equilibrium concentrations of our reagents and products, we have to work it out ourselves using the ICE method. First, we must write out the balanced equation.
Initial moles:
Change in moles:
Equilibrium moles:
So we know how many moles we have of each at equilibrium. Since we aren't given the concentration, we must assume that the number of mols equals the .
The equilibrium constant has no units as they cancel out: