Hello,
A.i. the circumference of a circle is nothing else but its perimeter which formula is π × diameter = π × 2 × radius
Let π = 22/7 ≈ 3.142857, the egyptian approximation
Then if C is the circumference of the circle i., C = 22/7 × 21 = (22 × 21) / 7 = (22× 7×3 )/7 = 22 ×3 = 66 cm
ii. Applying the same formula for the second circle gives us C = 22/7 × 8 = 176/7 ≈ 25.14 meters, rounded to the nearest hundredth...
Good luck !