This will get you going and probably finish you out. Much depends on your productivity of each plank.
I rounded off your dimensions to 288 square feet, then divided that by 21 square feet, this comes out to 13.71 packs, then add alittle for fudge, comes to 15. This may or may not be enough, but not too much at all.
If you want to buy a pack more and do not open it and keep the receipt and ask if they will return unopened packs with receipt, then you have nothing to loose and its good to have several planks on hand for those special damages that do happen. store those planks flat and on even surfaces.
If you are in doubt about laying this lam flooring down, please ask us about wall to floor gaps, and other stuff. This type of flooring does have problems with buckling later on down the road. Be sure you install it correctly.