Uncle Zhang surrounded the sheepfold. First, he surrounded a square sheepfold with a side length of 78.5 meters. Later, he found that it was not as big as a circle. Therefore, he used these fences to form the largest round sheepfold. The area of this round sheepfold is 200-200 square meters.

Solution steps: 78.5 * 4 = 314m314/6.28 = 50m50 * 50 * 3.14 = 7850m2.

Reference answer 7850