Hi everybody: i need your help to solve this issue about chemical equilibrium calculation

On this case my available datas are

Volume: 1 L

Temp: 25°C

Reaction (already balanced) --> N2 (g) + 3 H2 (g) 2 NH3 (g)

Moles of reagents and products (at equilibrium condition)

N2= 1 mol

H2 = 1,5 mol

NH3 = 1,8 mol

I need to:

- calculate equilibrium constant

- set up a new equilibrium equation (no need to solve) to determine new composition when 0,5 mol of NH3 are removed from the container

Basically i am stucked in a certain point and i can't go any further. I'd be really grateful to everyone who will reply and also will have the patience to explain step by step the method applied

Thanks a lot