Lesson 1 start time= 8:35
Lesson 1 start time plus 60 minutes
= Lesson 1 end time= 9:35
Lesson 2 start time= 9:35
Lesson 2 start time plus 60 minutes
= Lesson 2 end time= 10:35
Lesson 2 end time plus 15 min break
= Break= 10:50
Lesson 3 start time= 10:50
Lesson 3 start time plus 60 minutes
= Lesson 3 end time= 11:50
Lesson 4 start time= 11:50
Lesson 4 start time plus 60 minutes
= Lesson 4 end time= 12:50
ANSWER: Lesson 4 ends at 12:50
Hope this helps! :)