This is a text book, masters exam question. There are many more with the same result and the answer in the book is definelty showing 350a feeder fuse.
As far as the 'non time delay fuse' I think that is just thrown in there. You use that for rating motor 'branch circuits'. (short circuit, GFCI protection). I'm don't think its used in the feeder calcs. But I could be wrong.
