Question 1024336
Let's call the width, x, and length y.
.
.
Area,
1.{{{A=L*W=xy=80}}}
.
.
Perimeter,
{{{P=2(L+W)=2(x+y)=42}}}
2.{{{x+y=21}}}
From eq. 1,
{{{y=80/x}}}
Substituting into eq. 2,
{{{x+80/x=21}}}
{{{x^2+80=21x}}}
{{{x^2-21x+80=0}}}