Answer:15 ft
Step-by-step explanation:
Given
The total perimeter needed is [tex]40\ ft[/tex]
The available width of the room is [tex]w=5\ ft[/tex]
Suppose l is the length of the room
So, the perimeter of a rectangle-shaped room is [tex]2(l+w)[/tex]
Putting values
[tex]\Rightarrow 40=2(l+5)\\\Rightarrow l+5=20\\\Rightarrow l=15\ ft[/tex]