What is a Development Team responsible for?

A Product Owner wants advice from the Scrum Master about estimating work in Scrum. Which of these is the guideline that a Scrum Master should give?

What is the time-box for the Sprint Planning meeting?

A Scrum Master is keeping a list of open impediments, but it is growing and he/she has been able to resolve only a small portion of the impediments. Which three techniques would be most helpful in this situation?