Todd uses 21 white tiles & some black tiles to make a mosaic. The mosaic has a total area of 144 square centimeters. Each tile has an area of 3 square centimeters. How many black tiles did Todd use? Explain.

Answer: Todd used 27 black tiles.

Step-by-step explanation:

Let x represent the number of black tiles that Todd used.

Todd uses 21 white tiles & some black tiles to make a mosaic. This means that the total number of white and black tiles that Todd used is 21 + x

Each tile has an area of 3 square centimeters. This means that the total area covered by the white tiles is

21 * 3 = 63 square centimeters

Also, the total area covered by the black tiles is

3 * x = 3x square centimeters

The mosaic has a total area of 144 square centimeters. This means that

3x + 63 = 144

3x = 144 - 63

3x = 81

x = 81/3 = 27