A cow is tied with a 7 m long rope at each corner of a triangular field with sides of 26 m, 28 m and 30 m. Accordingly, how much m² will be the area of the field left by the grazing of those three cows?

Correct option is B

Given
Triangle sides: 26, 28, 30 m.
Rope length (r) = 7 m.

Solution
Area of Triangle (Heron's Formula):

​$$s = \frac{26+28+30}{2} = 42\\\ \\Area = \sqrt{42(42-26)(42-28)(42-30)} = \sqrt{42 \times 16 \times 14 \times 12} = 336 \text{ m}^2$$​​

Grazed Area = Area of 3 sectors with angles A, B, C.
​$$Total\ angle = 180^{\circ}\\\ \\Area = \frac{180}{360} \times \pi r^2 = \frac{1}{2} \times \frac{22}{7} \times 7 \times 7 = 77 \text{ m}^2\\\ \\Ungrazed\ Area = 336 - 77 = 259 \text{ m}^2$$​​

Final Answer
So the correct answer is (b)