The relation between the length and width is
[tex]l = w + 5[/tex]
Perimeter is 80.
[tex]80 = 2w \: + 2l[/tex]
Substitute the expression for l
[tex]80 = 2w + 2(w + 5)[/tex]
[tex]80 = 2w + 2w + 10[/tex]
[tex]70 = 4w[/tex]
[tex]w = 17.5 \: units[/tex]
[tex]l = 22.5 \: units[/tex]
