Final answer:
The correct formula to find the diameter of a circle from its circumference is d = c ÷ π, which involves dividing the circumference (c) by π. The options provided in the question are incorrect or incomplete. The correct option is c.
Step-by-step explanation:
The student is asking for the correct formula to find the diameter (d) of a circle when the circumference (c) is known, and the relationship between circumference and diameter is given by c = π d.
To find the diameter using the circumference, you rearrange this formula to solve for d: d = ÷ π. This means you divide the circumference by π to find the diameter.
Thus, the correct choice from the provided options is d = c ÷ π, which is not explicitly listed, but the concept equates to dividing c by π. The provided options are incorrect, and it seems there was a typo in option 4, which is incomplete. The correct option is c.