Lets split the box in pieces and then add: top = 20*15 = 300 sidesA = 2*20*9 = 360, is multiplied by 2 cause there are 2 sides like this sidesB = 2*9*15 = 270, is multiplied by 2 cause there are 2 sides like this so in total we have: total = 300 + 360 + 270 = 930 cm^2 if we express this quantity in mm^2 we have: <span>1cm² = 100 mm²</span>total = 930*100 = 93000 mm^2 so if the tiles are 5 mm^2 we need: total tiles = <span>93000/5 = 18600 we need 18600 tiles of 5 mm^2</span>
