Final answer:
The largest size squares Steve can purchase to cover the field without any gaps or overhang is 40 feet wide and 40 feet long.
Step-by-step explanation:
To determine the largest size squares Steve can purchase to cover the field completely without any gaps or overhang, we need to find the greatest common divisor (GCD) of the field's length and width.
In this case, the GCD of 360 and 160 is 40.
Therefore, the largest size squares Steve can purchase is 40 feet wide and 40 feet long, which would cover the field without any gaps or overhang.