How to add two columns and using its result for order by?

How to add two columns and using its result for order by?

I have this table
- ID Name Sub1 Sub2
- 1 Name1 99 89
- 2 Name2 78 90
What I want to happen is to query this given table and add the two
columns(sub1 and Sub2) and use their its for order by. How would I achieve
that? or an Idea how would I start this.