Answer: (x + 7)(x - 3) = 0
width (x) = 3
length (x+4) = 7
<u>Step-by-step explanation:</u>
Area (A) = length (l) × width (x)
21 = (x + 4) × (x)
21 = x² + 4x <em>distributed (x) into (x + 4)</em>
0 = x² + 4x - 21 <em>subtracted 21 from both sides</em>
0 = (x + 7)(x - 3) <em>factored quadratic equation</em>
0 = x + 7 or 0 = x - 3 <em>applied Zero Product Property</em>
x = -7 or x = 3 <em>solved each equation</em>
x = -7 is not valid <em>because lengths cannot be negative </em>
so x = 3
and length ... x + 4 = (3) + 4 = 7