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To find the Greatest Common Factor (GCF) of three numbers, I need to list the factors for each number in a set and identify the largest factor that appears in all three lists. Alternatively, I can use prime factorization or the Euclidean algorithm. For clarity and verification, I will work through each set step-by-step using the listing method or prime factorization to ensure accuracy.

Set 1: 24, 9, 15
- Factors of 24: 1, 2, 3, 4, 6, 8, 12, 24
- Factors of 9: 1, 3, 9
- Factors of 15: 1, 3, 5, 15
- Common factors: 1, 3
- GCF: 3

Set 2: 16, 20, 8
- Factors of 16: 1, 2, 4, 8, 16
- Factors of 20: 1, 2, 4, 5, 10, 20
- Factors of 8: 1, 2, 4, 8
- Common factors: 1, 2, 4
- GCF: 4

Set 3: 10, 20, 15
- Factors of 10: 1, 2, 5, 10
- Factors of 20: 1, 2, 4, 5, 10, 20
- Factors of 15: 1, 3, 5, 15
- Common factors: 1, 5
- GCF: 5

Set 4: 18, 6, 24
- Since 6 is a factor of both 18 ($6 \times 3$) and 24 ($6 \times 4$), the GCF must be 6.
- Verification: Factors of 18 include 6; Factors of 24 include 6. No larger number divides all three (next multiple of 6 is 12, which doesn't divide 18).
- GCF: 6

Set 5: 21, 7, 35
- Since 7 is a factor of 21 ($7 \times 3$) and 35 ($7 \times 5$), the GCF is 7.
- GCF: 7

Set 6: 20, 24, 12
- Factors of 20: 1, 2, 4, 5, 10, 20
- Factors of 24: 1, 2, 3, 4, 6, 8, 12, 24
- Factors of 12: 1, 2, 3, 4, 6, 12
- Common factors: 1, 2, 4
- GCF: 4

Set 7: 10, 18, 8
- Factors of 10: 1, 2, 5, 10
- Factors of 18: 1, 2, 3, 6, 9, 18
- Factors of 8: 1, 2, 4, 8
- Common factors: 1, 2
- GCF: 2

Set 8: 20, 12, 8
- Factors of 20: 1, 2, 4, 5, 10, 20
- Factors of 12: 1, 2, 3, 4, 6, 12
- Factors of 8: 1, 2, 4, 8
- Common factors: 1, 2, 4
- GCF: 4

Set 9: 9, 15, 21
- Factors of 9: 1, 3, 9
- Factors of 15: 1, 3, 5, 15
- Factors of 21: 1, 3, 7, 21
- Common factors: 1, 3
- GCF: 3

Set 10: 12, 9, 15
- Factors of 12: 1, 2, 3, 4, 6, 12
- Factors of 9: 1, 3, 9
- Factors of 15: 1, 3, 5, 15
- Common factors: 1, 3
- GCF: 3

Set 11: 12, 24, 36
- Since 12 divides 24 ($12 \times 2$) and 36 ($12 \times 3$), the GCF is 12.
- GCF: 12

Set 12: 60, 45, 30
- Factors of 60: ..., 15, 20, 30, 60
- Factors of 45: ..., 15, 45
- Factors of 30: ..., 15, 30
- Check 15: $60 \div 15 = 4$, $45 \div 15 = 3$, $30 \div 15 = 2$. All divide evenly.
- Next possible common factor would need to be larger than 15. 30 does not divide 45.
- GCF: 15

Set 13: 24, 60, 48
- Prime factorization:
- $24 = 2^3 \times 3$
- $60 = 2^2 \times 3 \times 5$
- $48 = 2^4 \times 3$
- Common primes: $2^2 \times 3 = 4 \times 3 = 12$
- GCF: 12

Set 14: 32, 72, 64
- Prime factorization:
- $32 = 2^5$
- $72 = 2^3 \times 3^2$
- $64 = 2^6$
- Common primes: lowest power of 2 is $2^3 = 8$
- GCF: 8

Set 15: 60, 50, 40
- All end in 0, so 10 is a factor.
- $60 \div 10 = 6$
- $50 \div 10 = 5$
- $40 \div 10 = 4$
- GCF of 6, 5, 4 is 1.
- So GCF is $10 \times 1 = 10$.
- GCF: 10

Set 16: 52, 26, 13
- 13 is prime.
- $26 \div 13 = 2$
- $52 \div 13 = 4$
- Since 13 divides all three, and it is the largest factor of itself, GCF is 13.
- GCF: 13

Set 17: 84, 14, 49
- Factors of 14: 1, 2, 7, 14
- Factors of 49: 1, 7, 49
- Common factors of 14 and 49: 1, 7
- Check if 7 divides 84: $84 \div 7 = 12$. Yes.
- Check if 14 divides 84: $84 \div 14 = 6$. Yes. But 14 does not divide 49.
- So GCF is 7.
- GCF: 7

Final Answer:
Here are the Greatest Common Factors for each set of numbers:

* 24, 9, 15: 3
* 16, 20, 8: 4
* 10, 20, 15: 5
* 18, 6, 24: 6
* 21, 7, 35: 7
* 20, 24, 12: 4
* 10, 18, 8: 2
* 20, 12, 8: 4
* 9, 15, 21: 3
* 12, 9, 15: 3
* 12, 24, 36: 12
* 60, 45, 30: 15
* 24, 60, 48: 12
* 32, 72, 64: 8
* 60, 50, 40: 10
* 52, 26, 13: 13
* 84, 14, 49: 7