Question

the perimeter of the unknown length

Answer 1

perimeter is equalt to 2l+2w where l is the length and w is the width
or l+l+w+w 
so if the perimeter is 14 feet
and the length is 4 feet
14= 4+4+r+r
14= 8+ 2r 
6=2r
r=3 
the length of one side is 3 feet