In five rounds, Jackson covers a distance of 300 m, which is equal to five times the perimeter of the square garden.
Let the side length of the garden be x, then perimeter =4x
Now, total distance covered in five rounds = 300
⇒5×Perimeter =300
⇒5×4x=300
⇒20x=300
Divide both sides by 20
⇒20x20=30020
⇒x=15 m
Hence, the side length of the garden is 15 m.