The difference between the area of a circular field and the area of a square field is 168 sq m. The side of the square field is equal to the diameter of the circular field. What is the cost of fencing the square field at the rate of 20 per metre?

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**Solution:**

1. Let the side of the square be *a* metres and the radius of the circle be *r* metres.

2. Given that the side of the square equals the diameter of the circle:
   $$a = 2r$$

3. The difference between the area of the square and the circle is 168 sq m:
   $$a^2 - \pi r^2 = 168$$

4. Substitute $a = 2r$:
   $$ (2r)^2 - \pi r^2 = 168 $$
   $$ 4r^2 - \pi r^2 = 168 $$

5. Using $\pi = \frac{22}{7}$:
   $$ 4r^2 - \frac{22}{7} r^2 = 168 $$

6. Multiply both sides by 7 to clear the denominator:
   $$ 28r^2 - 22r^2 = 168 	imes 7 $$
   $$ 6r^2 = 1176 $$

7. Solve for $r^2$:
   $$ r^2 = \frac{1176}{6} = 196 $$

8. Find $r$:
   $$ r = \sqrt{196} = 14 	ext{ m} $$

9. Find the side of the square:
   $$ a = 2r = 2 	imes 14 = 28 	ext{ m} $$

10. Calculate the perimeter of the square:
    $$ 4a = 4 	imes 28 = 112 	ext{ m} $$

11. Calculate the cost of fencing at 20 per metre:
    $$ 112 	imes 20 = 2240 $$

**Answer:** 2,240/-

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