Answer:
42
Step-by-step explanation:
The factors of 42 (all the whole numbers that can divide the number without a remainder) are 1, 2, 3, 6, 7, 14, 21 and 42;
The factors of 84 are 1, 2, 3, 4, 6, 7, 12, 14, 21, 28, 42 and 84.
Which one is in both and is the highest number;
42