2015 Macbook or Macbook air?

16 years old, trying to pick a new notebook: Following requirements:

-Portable -Good screen and display -Price cannot exceed £1400 -Used mainly for word, powerpoint and excel but may need to do photo editing on occasion -Needs to last 3 years at least -Any other things you can think of a secondary school, soon to be college would need, mainly interested in maths and sciences as subjects.

Thanks