Question

Brenda is making a dessert that takes 3.5 hours to prepare. If she wants to be finished by 1:15, at what time should she start??

Answer 1

3.5 hours is 3 hours and 30 minutes.
1:15 is 1 hour and 15 minutes. 

The question is asking at what time does she want to start and end up at 1 hour and 15 minutes? SO you add the time it takes for her to make the dessert with the time at which she ends.

TLTR?? 4:45