GCSE Redox Reaction (involving rusting of iron) Watch

SO I am using the CGP OCR Gcse Chemistry revision guide and is says:

That the rusting of iron is a redox reaction: iron+oxygen+water > hydrated iron(iii) oxide
The explanation in the book is:
1) Iron loses electrons when it reacts with oxygen. Each Fe atom loses three electrons to become Fe3+
2) Oxygen gains electrons when it reacts with iron. Each O atom gains two electrons to become O2-

So, could you please explain the following to me:
1) Why each Iron Fe atom lose three electrons when it reacts with oxygen?
2) If three electrons are lost from the Iron to become Fe3+, why does each Oxygen O atom only gain two electrons to become O2-? Surely it should gain 3 electrons since 3 are lost from the iron?

Thank you so much