A rope with a length of 3 14m forms a circle, that is, the circumference = 3 14m.

According to pi formula: 2πr=3 14, radius r = 50m.

Area = π r 2 = 3. 14 * 50 * 50 = 7850 square meters.

* * * Harvesting weeds = 7850 * 40 = 314000kg = 314 (ton)