Answer:1. 15 and 45 - Factors of 15: 1, 3, 5, 15- Factors of 45: 1, 3, 5, 9, 15, 45- GCF: 15 (The largest number that divides into both 15 and 45) 2. 28 and 36 - Factors of 28: 1, 2, 4, 7, 14, 28- Factors of 36: 1, 2, 3, 4, 6, 9, 12, 18, 36- GCF: 4 (The largest number that divides into both 28 and 36)