The first thing you need to do is figure this out...
5/8 = __/112
=5/8 = 70/112 because 112/8 = 14, so you just had to do 5*14
Now we know that 70 people out of 112 were served chocolate cake, but we want to know how many people got carrot cake.
So now all you have to do is 112 - 70 to get 42
Answer: 42 people were served carrot cake