Calculate the area of a circle with radius 20cm, diameter 28cm, and area 145 cm2. Find its radius.

$$A = \pi r^2$$ $$A = \frac{22}{7} \times (20 \text{ cm})^2$$ $$A = \frac{22}{7} \times 400 \text{ cm}^2$$ $$A = \frac{8800}{7} \text{ cm}^2$$

$$A \approx 1257.14 \text{ cm}^2$$

The area of the circle is $\boxed{\text{1257.14 cm}^2}$.

2. Find the area of a circle whose diameter is 28cm.

$$d = 28 \text{ cm}$$ $$r = \frac{d}{2} = \frac{28 \text{ cm}}{2} = 14 \text{ cm}$$

$$A = \pi r^2$$ $$A = \frac{22}{7} \times (14 \text{ cm})^2$$ $$A = \frac{22}{7} \times 196 \text{ cm}^2$$

$$A = 22 \times 28 \text{ cm}^2$$ $$A = 616 \text{ cm}^2$$

The area of the circle is $\boxed{\text{616 cm}^2}$.

3. The area of a circle whose is 145cm. Calculate its radius.
(Assuming the question means "The area of a circle whose area is 145 cm$^2$")

$$A = \pi r^2$$ $$145 \text{ cm}^2 = \frac{22}{7} r^2$$

$$r^2 = \frac{145 \times 7}{22} \text{ cm}^2$$ $$r^2 = \frac{1015}{22} \text{ cm}^2$$ $$r = \sqrt{\frac{1015}{22}} \text{ cm}$$

$$r \approx \sqrt{46.136} \text{ cm}$$ $$r \approx 6.79 \text{ cm}$$

The radius of the circle is $\boxed{\text{6.79 cm}}$.

4. The diameter of the clock face on a town hall is 30cm. Find area of the clock face to the 1 cm.

$$d = 30 \text{ cm}$$ $$r = \frac{d}{2} = \frac{30 \text{ cm}}{2} = 15 \text{ cm}$$

$$A = \pi r^2$$ $$A = \frac{22}{7} \times (15 \text{ cm})^2$$ $$A = \frac{22}{7} \times 225 \text{ cm}^2$$

$$A = \frac{4950}{7} \text{ cm}^2$$ $$A \approx 707.14 \text{ cm}^2$$

Rounding to the nearest 1 cm$^2$:

$$A \approx 707 \text{ cm}^2$$

The area of the clock face is $\boxed{\text{707 cm}^2}$.

5. Find the area of the circular web of a spider if the radius is 1.4cm.

$$A = \pi r^2$$ $$A = \frac{22}{7} \times (1.4 \text{ cm})^2$$ $$A = \frac{22}{7} \times 1.96 \text{ cm}^2$$

$$A = 22 \times 0.28 \text{ cm}^2$$ $$A = 6.16 \text{ cm}^2$$

The area of the circular web is $\boxed{\text{6.16 cm}^2}$.

6. What is the area of a circle of radius 3.5cm?

$$A = \pi r^2$$ $$A = \frac{22}{7} \times (3.5 \text{ cm})^2$$ $$A = \frac{22}{7} \times \left(\frac{7}{2}\right)^2 \text{ cm}^2$$

$$A = \frac{22}{7} \times \frac{49}{4} \text{ cm}^2$$ $$A = \frac{22 \times 7}{4} \text{ cm}^2$$ $$A = \frac{154}{4} \text{ cm}^2$$ $$A = 38.5 \text{ cm}^2$$

The area of the circle is $\boxed{\text{38.5 cm}^2}$.