This is I suppose basic addition. Addition is a mathematical process of combining or joining something to something else. The word "total" indicates that the addition will be used. If the doctor ran for 55 hours and the mom for 52 hours, by using the addition it will be:
55
+ 52
______
107 hours in total.
107 hours converted in days will be 4 days and 4 hours. SInce 1 day contains 24 hours you now divide 107 hours by 24 hours to get its equivalent to days.