what is the factor of 200?
what is the factor of 99?
Both numbers have more than one factor. I suggest you try dividing 200 by 5 as many times as you can, until you no longe get an integer for a quotient.
200/5 = 40
40/5 = 8 etc. Then do the same to 8 with 2 as a factor
With 99, do the same with the number 3. Let us know what you get.