In this case, we want to write an expression representing the number of hours Anna has volunteered. The key phrase in the sentence is ... more ... than ... This indicates that we should add two things.
... + ...
The two terms that we are adding together are 9 and the hours Tricia has volunteered. Let t represent the number of hours Tricia has volunteered. Even though 9 comes first in the sentence, it can be on the right-hand side of the addition.
t + 9
Note that this is only one of the multiple ways to algebraically express the given verbal expression.
