My answer is 28 = 2: 8. 
That means that the ratio 7 / 28 is equal to the ratio 2 : 8. 
You can verify the equality by simplifying to the simplest form:
     7 : 28 = 1 / 4 simplest form
     2 : 8 = 1 / 4 simplest form, then the proportion is right.
In words that is 7 is to 28 as 1 is to 4 ← answer