Call x the percentage of Carrie's time that is spent on maintenance. We can write the following equation to solve for x: x+15+30=100, and subtracting 45 from both sides, we get x=55. Therefore, 55% of Carrie's time is spent on maintenance.
Notice that how much time Carrie spends at work is extraneous information. Remember, just because a problem gives you certain information doesn't mean you need to use the information to solve the problem!