Answer:
14
Explanation:
To calculate the greatest common factor (GCF) of 28 and 42, we need to factor each number (factors of 28 = 1, 2, 4, 7, 14, 28; factors of 42 = 1, 2, 3, 6, 7, 14, 21, 42) and choose the greatest factor that exactly divides both 28 and 42, i.e., 14.