we know that
perimeter of a rectangle=2*[length+width]
let
x----------> the length
y----------> the width
so
P=60 ft
60=2*[x+y]---------> x+y=30
the length and the width may be all pair of numbers whose sum is equal to 30 feet
example
x=10 ft
y=20 ft
P=2*[10+20]----> 60 ft
The lot could be 10 feet by 20 feet.
x=15 ft
y=15 ft
P=2*[15+15]----> 60 ft
The lot could be 15 feet by 15 feet.
x=5 ft
y=25 ft
P=2*[5+15]----> 60 ft
The lot could be 5 feet by 25 feet.