Given data:
The expression for length is L= 3b.
The perimeter of the rectangle is P = 80 cm.
The expression for the perimeter is,
[tex]P=2(L+b)[/tex]Substitute the given values in the above expression.
[tex]\begin{gathered} 80\text{ cm =2(3b+b)} \\ 80\text{ cm=8b} \\ b=10\text{ cm} \end{gathered}[/tex]The length of the rectangle is,
[tex]\begin{gathered} L=3(10\text{ cm)} \\ =30\text{ cm} \end{gathered}[/tex]Thus, the length of the rectangle is 30 cm, and width of the rectangle is 10 cm.
