What is the greatest common factor of 63 and 84?

Step 1: First, we need to find the prime factors of each number.

For 63, the prime factors are 3, 3, and 7 (because 337 = 63).

For 84, the prime factors are 2, 2, 3, and 7 (because 223*7 = 84).

Step 2: Now, we find the common prime factors between the two numbers.

The common prime factors are 3 and 7.

Step 3: The greatest common factor (GCF) is the product of the common prime factors.

So, the GCF of 63 and 84 is 3*7 = 21.