The Reaction can be represented as 

                         N2+3H2=2NH3

Let x mol of N2 Got reacted till equilibrium is reached, then According to stoichiometry, Moles of the component Present at equilibrium.

N2=1-x

H2=3-3x

NH3=2x

Then Equilibrium Constant 

K=(2x)^2/27(1-x)^3=4/27

therefore   x/(1-x)^2=1

Now You can calculate the X and hence the corresponding concentration at Equilibrium.