1. The problem asks us to identify which number among 6, 28, 10, and 12 is not a perfect number. 2. A perfect number is a positive integer that is equal to the sum of its proper divisors (excluding itself). 3. Let's check each number: - For 6: Proper divisors are 1, 2, 3. Sum = $1 + 2 + 3 = 6$. So, 6 is perfect. - For 28: Proper divisors are 1, 2, 4, 7, 14. Sum = $1 + 2 + 4 + 7 + 14 = 28$. So, 28 is perfect. - For 10: Proper divisors are 1, 2, 5. Sum = $1 + 2 + 5 = 8$. Since 8 $\neq$ 10, 10 is not perfect. - For 12: Proper divisors are 1, 2, 3, 4, 6. Sum = $1 + 2 + 3 + 4 + 6 = 16$. Since 16 $\neq$ 12, 12 is not perfect. 4. Among the options, 10 and 12 are not perfect numbers, but since the question asks for which is not a perfect number, the first such number is 10. Final answer: 10 is not a perfect number.