Final answer:
To factor 21c + 24, the greatest common factor is 3. The factored form is 3(7c + 8).
Step-by-step explanation:
To factor 21c + 24, we need to find the greatest common factor of the two terms. In this case, the greatest common factor is 3. So, we can factor out 3 to get: 3(7c + 8).