Find the length and width of the rectangle

The length of a rectangle is 3 times the width. The area is 48 square feet. Find the length and width of the rectangle.

x = width
3x = length {length is 3 times the width} 

Area of a rectangle = length x width 

x(3x) = 48   {substituted length and width into area formula}
3x² = 48   {multiplied}
x² = 16   {divided each side by 3}
x = 4 or -4   {took square root of each side} 

x = 4   {width cannot be negative}
3x = 12   {substituted 4, in for x, into 3x} 

width = 4 ft
length = 12 ft

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