1:15 pm, remove the set the 15 aside so its 1:00.

2 hours and 20 minutes, 2:20. set the 20 aside and its 2 hours only.

1:00pm – 2 hours = 11:00

Check: 1:00 → 12:00 → 11:00 ( The time is Decreasing )

11:00 + 2:00 = 13:00 which means 1:00

20 – 15 = 5

11:00 – 5 = 10:55

Marie start working at 10:55

The solution is really messy but the question is not asking the solution so it's fine.