Hardwood finish repair advice needed.

[bigdog]

I have to refinish a few spots on my kitchen hardwood floor.

The issue was there when I purchased the house a few years ago, and just getting around fixing. I believe the issue was a result of a 'rolling cart',
moving back and forth which wore the finish completely off the hardwood.

There are two spots on either side of kitchen island. Areas look like the 'finish' has been worn off the wood, each area about 6-8" long, and across two strips/planks of hardwood.

So looking for suggestions about refinish.... Obviously I need to sand the wood first, what grade sandpaper ? The wood is not stained, but has clear urethane not oil. So looking to use a 'water based' urethane for quick drying time.

I had a flooring repair/install company review, but they said it wasn't worth their time.

All your suggestions will be greatly appreciated, thanks !