Question: Calculate the circumference of this circle.
Give your answer in terms of $\pi$.
$42$ mm
Graph: A circle centered near the lower-middle of the page with a radius line from the center to the lower-left edge labeled $42$ mm; position_hint = center.
1. **State the problem:** We need to calculate the circumference of a circle with radius $42$ mm, and express the answer in terms of $\pi$.
2. **Formula for circumference:** The circumference $C$ of a circle is given by the formula:
$$C = 2 \pi r$$
where $r$ is the radius of the circle.
3. **Substitute the radius:** Here, $r = 42$ mm, so:
$$C = 2 \pi \times 42$$
4. **Calculate the product:**
$$C = 2 \times 42 \pi = 84 \pi$$
5. **Final answer:** The circumference of the circle is:
$$\boxed{84 \pi \text{ mm}}$$
This means the circumference is $84$ times $\pi$ millimeters.