Answer:
60 in
Explanation:
We are given that 
Steve built a square dog pen of perimeter=240 in
We have to find the length of one side of Steve's dog pen.
To find the value of length of Steve's side we will use the formula of perimeter of square.
We know that 
Perimeter of square=

Substitute the values in the given formula 


Length of Steve' s dog pen=60 in
Hence, the length of one side of Steve's dog pen=60 in