Let h be the number of hours that pass when Charlie starts. We have the following equations:

- Charlie: D = 40h + 9
- Danny: D = 55h

Set them equal to each other:

40h + 9 = 55h

Subtract 40h from both sides:

15h = 9

h = 3/5

**3/5 of an hour = 3(60)/5 = 36 minutes**