The perimeter of a square is the sum of all sides. Since a square has 4 sides, you have to divide 1/5 meters (0.2m) by 4
1/5 ÷ 1/4 = 1/20 (you're basically multiplying the denominators, as the numerator has to be divided by 5 and then 4)
Or 0.2 ÷ 5 = 0.04