The answer is D. 2.0 because you start with 4.23 8.91 and 15.12 when it says round each number to the nearest tenth you round every number on the page now you have: 4.2, 8.9, and 15.1t hen you add 4.2 and 8.9 and get 13.1
now all you have to do is subtract 15.1 - 13.1= 2.0 or 2 and that is why D. is the answer
hope this helps