First you want to break down both numbers to prime factors so for 10 you would get 10=2x5 and 14 you would get 14=2x7 then you will want to take the greatest common factor of both which is 2 because it is the only factor that is shared between the two then you take the two beginning numbers and divide them by 2 because it is the greatest common factor and 5/7 is your anwser
