divide the 256 by 144 and you get 1.778 sq foot per tile
divide 350 sq feet by 1.778 and you will know how many tiles
196.875 is the exact calculation, if this is Homework
If this is a real flooring exercise, there is the grout line and the fact that 16X16 tiles are not fully 16X16 so you have to allow a few extra for trim & finish.