Final answer:
The statement translates to the inequality 3x - 7 ≥ 21 where x is the unknown number. This indicates that seven less than three times a number should be at least twenty-one, setting the inequality option as 'is at least seven hours.'
Step-by-step explanation:
To translate the statement 'Seven less than 3 times a number is at least twenty-one' into an inequality, let's define the variable x as the unknown number. Three times the number can be represented as 3x. Seven less than this amount is 3x - 7. The phrase 'at least twenty-one' indicates that this amount is greater than or equal to 21, which leads to the inequality 3x - 7 ≥ 21.
To find the corresponding inequality from the available options, we simply choose the one that matches our translated inequality, which is 3x - 7 ≥ 21. Therefore, the correct option is:
- c. is at least seven hours.