Question

if the width of a rectangle is 5 inches shorter than the length and the perimeter of the rectangle is 80 inches.

how do you set up the equation for the perimeter involving only L and how do you solve this in a linear equation algebraically to find the length and the width

Answer 1

let the length be L
"..the width of a rectangle is 5 inches shorter than the length"
so width = L - 5

Twice the width + twice the length = 80
2L + 2(L-5) = 80

take it from there.
once you have L, evaluate L-5 for the width