Answer:
50 minutes 
Explanation:
she spent 1 hr and 30 minutes on homework 
she spends 2/3 of an hour on the phone = 40 minutes 
1 hr 30 min + 40 minutes = 2 hrs and 10 min 
so she had 50 minutes to kill before bedtime since she goes to sleep 3 hrs after dinner 
2hr 10 min + 50 min = 3 hrs.