Chemistry Help? Determine the amount if oxygen needed to burn the magnesium. Show full calculations Write a balanced chemical equation of it?

Here is the question: a student carried out an experiment to examine the burning of magnesium metal. The mass of the piece of magnesium is 3.0 grams. The student burns it, being careful to collect all the pieces of white ash that are produced. The student determines the masks of the ash is 5.0 grams.

a) determine the amount of oxygen needed to burn the magnesium. Show full calculation

b) write a balanced chemical equation for this reaction.