What is the gcf of 54 and 42?

The greatest common factor (GCF) of 54 and 42 is 6. This is because 6 is the largest number that divides both 54 and 42 without leaving a remainder. The prime factors of 54 are 2, 3, and 3, while the prime factors of 42 are 2, 3, and 7. The GCF is found by taking the smallest power of each prime factor that appears in both numbers, which in this case is 2 * 3 = 6.