Answer:
50 minutes left.
Explanation:
The easiest way to do this is to convert all the fractions into minutes
So, she would've spent 1 hour and 30 minutes on her homework and 40 minutes on her telephone. If you add those amounts up, you get 2 hours and 10 minutes. Since she goes to bed 3 hours after dinner, and 2 hours and 10 minutes have gone by, you do 3 hours - 2 hours 10 minutes and you get 50 minutes.
Hope that makes sense. Let me know if you have any questions.