We are given "Ann earns $5000 more per year than Bill".
We are not given any value for a Bill. So we can take a variable for a bill amount.
Let us assume amount of each bill = $x.
Now, we can make a statement " Ann earns $5000 more per year than x.", because x is representing bill amount there.
Now, we can make an expression for it.
Ann earning = 5000+x.
Because for " more " word, we use addition operation when writing expressions.
