Let:
x cm be the width, and
x + 20 cm be the length.
A = 2400
A = lw
2400 = (x + 20)(x)
2400 = x² + 20x
x² + 20x - 2400 = 0
(x + 60)(x - 40) = 0
x + 60 = 0 | x - 40 = 0
x = -60 | x = 40
*We can't use -60, since there's no measurement such as negative. Therefore, the value of x is 40, then, the width is 40.
x = 40 cm
Length:
x + 20 cm = 40 cm + 20 cm = 60 cm
The width is 40 cm and the length is 60 cm.
