Math
posted by pretty .
Kate's plane leaves at 3:35 P.M. She has to check in 2 h and 35 min to get to the airport from her home. Kate must first drop off her dog, Fido, at her friend's house next door. She wants to spend 45 min talking to her friend. What is the latest time she should leave her house?
Thank you!

Please proofread this sentence and repost. As it is, it doesn't make sense.
She has to check in 2 h and 35 min to get to the airport from her home. 
I think there is a typo in your question. "She has to check in 2 h and 35 min". Is it she has to check in 2 hours early and it takes 35 minutes to get to the airport?
If so, you want to add up all the time for travel and chit chat. So 2 hours + 35 minutes + 45 minutes, and then make sure she leaves her house that much earlier than 3:35. 
She has to check in 2 h before takeoff.
This one is correct. 
12:15

Kate's plane leaves at 3:35 P.M. She has to check in 2 h before takeoff. She takes 1h and 35 min to get to the airport from her home. Kate must first drop off her dog, Fido, at her friend's house next door. She wants to spend 45 min talking to her friend. What is the latest time she should leave her house? For this can you show formula how to do it?