At 9 s/f per box yes you ll need 3x36=108..108x12=1296 sq inches..1296 divided by 144( sq/i per sq/f) =9.

9 into 120 s/f is 22.22as one person said but you ll need more than one extra box. To get all the scrap you ll need at least 23 possible 24 boxes..You won t create much scrap if you start and use your cut off pcs correctly.. GL

20 years in flooring as a store owner/installler

1 box = 12 sf. Room is 200 sf. 200÷12= you will trim boards to randomize.

The area of one plank is 3ft by .25 = .75sq feet

area covered by box of planks 9sq feet

area of room 200 sq feet.

so you need 22.22 boxes

or 23 boxes with a couple of planks spare.