Charlie should order 22 boxes of floor tiles.

Step 1
Draw a diagram of the space.

Step 2
Find the area of the space. Separate the space into a triangle and a rectangle.

• Find the area of ABCE.
  Use the formula A = lw.
  A = 20 ft x 8 ft
  Area of rectangle ABCE = 160 ft²
  
• Find the area of the triangle AED.
  se the formula A = bh.
  A = 1/2 20 x 8
  Area of triangle AED = 80 ft²
  
• Add the areas of ABCE and AED.
  160 ft² + 80 ft²= 240 ft²

• 1 tile = 1 square foot This means that for each square foot of floor space, Charlie needs 1 tile. For 240 ft² of floor space, Charlie will need 240 tiles.
• Add 2 dozen extra tiles for replacements. 240 tiles + 24 tiles = 264 tiles
• The tiles come in boxes of a dozen.
• Divide. 264 tiles ÷ 12 = 22 boxes of tiles