The area of a square garden is 1 / 81 km^2. How long is each side?

Km^2 = 1,000,000 meters

1,000,000 meters divided by 81 is 12345.679

the square root of 12345.679 square meters is 111.111

111.111 meters is a single side of the garden.

111.111^2 = 12345.654

12345.654 * 81 = 999,997.974