So you have to figure out what the variable is, for example: The question #6 says 10/18 = n/9. Divide by 2 for 10 and 18 and you get 5/9, so N = 5
Or you could do 18 x N = 18n and 10 x 9 which is 90, then divide 90 by 18 which is 5.
6.) N = 5
10.) D = 7
14.) N = 4