Answer:
4  hours and  57  minutes.
Step-by-step explanation:
The least common multiple of  9  and  11  is  99
.  
In  99  hours, Sue could fill  11 orders (99 divided by 11)
Felipe could fill 9  orders (
99  divided by 11
), making a total of  
9
+
11
=
20  orders if they both work.
So for both of them working to fill one order would take:  
99
/20  hours.
To express in hours and minutes:
99
/20
=
80
/20
+
19
/20
=
4
+  3
⋅
19
/3
⋅
20
=
4
+  57
/60
That's  4  hours and  57  minutes, since a sixtieth of an hour is one minute.