From the statement, we know that:
• Santa assigned Mrs Claus four hours of housework,
,• Rudolph gave Mrs Claus five hours of outside work.
So 5 + 4 = 9 hours of work has been assigned to Mrs Claus.
I think that we have two possible answers.
1) One answer could be that no hours of free time have been added, only working hours have been assigned.
2) Another answer could be that, if the tasks assigned to Mrs Claus must be done each day, Mrs Claus will have 24 - 9 = 15 hours of free time each day.