Area of a rectangle with length, l and breadth, b = <span>l⋅b</span>
Given <span>l=2b+8</span> and <span>A=120</span>
Area A = <span>l⋅b=<span>(2b+8)</span>⋅b=2<span>b2</span>+8b=120</span> =>
<span><span>2<span>b2</span>+8b−120=0</span> =><span><span>b2</span>+4b−60=0</span> =><span><span>b2</span>+10b−6b−60=0</span> =><span>b<span>(b+10)</span>−6<span>(b+10)</span>=0</span> =><span><span>(b−6)</span><span>(b+10)</span>=0</span>; =><span>b=6</span> as b cannot be <span>−10</span>.</span>
