Calculate the circumference of circles given their radius or diameter.

$$C = 2 \times 22 \text{ cm}$$ $$C = 44 \text{ cm}$$

The circumference is $\boxed{\text{44 cm}}$.

b) Diameter $d = 21$ cm

$$C = 22 \times 3 \text{ cm}$$ $$C = 66 \text{ cm}$$

The circumference is $\boxed{\text{66 cm}}$.

c) Diameter $d = 4$ cm

$$C = \frac{88}{7} \text{ cm}$$

The circumference is $\boxed{\frac{88}{7} \text{ cm}}$ or approximately $\boxed{\text{12.57 cm}}$.

2. Calculate the circumference of a circle whose:

a) radius is 9 cm

$$C = \frac{44 \times 9}{7} \text{ cm}$$ $$C = \frac{396}{7} \text{ cm}$$

The circumference is $\boxed{\frac{396}{7} \text{ cm}}$ or approximately $\boxed{\text{56.57 cm}}$.

b) diameter is 3.5 m

$$C = \frac{22}{7} \times \frac{7}{2} \text{ m}$$ $$C = 11 \text{ m}$$

The circumference is $\boxed{\text{11 m}}$.

3. A circular garden is 21 m in diameter. Find the length of wire required to fence the garden.

Use the formula $C = \pi d$.

$$C = \frac{22}{7} \times 21 \text{ m}$$

$$C = 22 \times 3 \text{ m}$$ $$C = 66 \text{ m}$$

The length of wire required is $\boxed{\text{66 m}}$.

4. The length of a minute hand of a clock is 12cm. Find the distance that the tip of the minute hand moves in 60 minutes. (Take $\pi = 3.14$).

The distance moved by the tip is the circumference of the circle traced by the minute hand. The length of the minute hand is the radius $r = 12$ cm. Use the formula $C = 2\pi r$.

$$C = 2 \times 3.14 \times 12 \text{ cm}$$

$$C = 24 \times 3.14 \text{ cm}$$ $$C = 75.36 \text{ cm}$$

The distance the tip moves is $\boxed{\text{75.36 cm}}$.

5. If the circumference of a circle is 154cm. Find its radius.

$$r = \frac{154 \times 7}{44} \text{ cm}$$ $$r = \frac{1078}{44} \text{ cm}$$ $$r = 24.5 \text{ cm}$$

The radius is $\boxed{\text{24.5 cm}}$.

6. Find the diameter of a circle whose circumference is 66cm.

$$d = 3 \times 7 \text{ cm}$$ $$d = 21 \text{ cm}$$

The diameter is $\boxed{\text{21 cm}}$.