Help me fix this leak

[Plumbing newbie]

Hi

Would someone know how I fix this leak, the arrow shows where the water is coming from. My concern is that part b might be welded/soldered to part the copper pipe labeled c,.

I’ve tried Shelley’s aqua putty, to just cover all the threads/join but other than making way more work for me, I’m not sure it’s done much

https://*********/a/cYyGVSI

Thanks a million in advance

 

[Deleted member 120897]

Sorry, link doesn’t work, as it’s not complete? and no photo(s).