15 : 7 : : 60 : x
Find x in the following proportion

15 : 7 :: 60 : x
Product of extremes = 15x

Product of means     = 7 x 60
                               
15x =  7 x 60
x =  7 x 60 
         15
x =  7 x 60 4
          15  1
x = 7 x 4 
  = 28
Therefore, x = 28