Question: give me one exercise about the circumference
1. **Problem Statement:** Calculate the circumference of a circle with radius $r = 7$ units.
2. **Formula:** The circumference $C$ of a circle is given by the formula:
$$C = 2 \pi r$$
where $\pi$ is approximately $3.1416$ and $r$ is the radius of the circle.
3. **Calculation:** Substitute $r = 7$ into the formula:
$$C = 2 \pi \times 7$$
4. **Simplify:**
$$C = 14 \pi$$
5. **Approximate:** Using $\pi \approx 3.1416$,
$$C \approx 14 \times 3.1416 = 43.9824$$
6. **Answer:** The circumference of the circle is approximately $43.98$ units.