Perimeter of a rectangle

The perimeter of a rectangle is 60 cm.  Its length is 12 cm what is its width?

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Perimeter of a rectangle = 2(width)  + 2(length)

60 = 2w + 2(12)  {substituted perimeter and length into perimeter formula}
60 = 2w + 24   {multiplied 2 by 12}
2w = 36  {subtracted 24 from each side}
w = 18   {divided each side by 2}

width = 18 cm

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