Answer:
I cost no money to use, or conscious effort to take part of. And as far as you can see, there is nothing to me. But without me, you are dead.
Hard to catch, easy to hold. Can't be seen, unless it's cold.
What is often returned but is never borrowed?
The sharp slim blade, that cuts the wind. What is it?
Reaching stiffly for the sky, I bare my fingers when its cold. In warmth I wear an emerald glove and in between I dress in gold.
How can you add eight 6s together so that the total adds up to 750?