1. **State the problem:** Find the greatest common factor (GCF) of the numbers 12 and 28. 2. **Recall the formula and rules:** The GCF of two numbers is the product of the lowest powers of all prime factors common to both numbers. 3. **Prime factorization:** - 12 = $2^2 \cdot 3$ - 28 = $2 \cdot 7$ 4. **Identify common prime factors:** Both have the prime factor 2. 5. **Choose the lowest power of common primes:** For 2, the lowest power is $2^1$. 6. **Calculate the GCF:** $$\text{GCF} = 2^1 = 2$$ 7. **Answer:** The greatest common factor of 12 and 28 is 2.