My question is how much does 1

As I said, it is really hard to count it, because it depends on luck a lot.
But I would say with 100MHs you can find a 1-2 blocks (17NXS per block) per day and one Radeon R9 390 can do aprox. 40Mhs (you get more particular numbers if you let the miner run for a while).

from where you calculated that? the diff in this coin is confusing, i can't tell if the nethash is 300GH or that is the diff, it say "hashdiff" in getminigninfo
I didn't do any particular calculation, the number was just based on my experience and on numbers from other people from slack.
There was a solo mining guy with a 100MHs with an average rate of 1-3 blocks per day, some other guy had 150MHs with 3-5 blocks per day.
But the diff jumps a lot, so during last two weeks it was even less than this. Right now the diff is 280, but a few hours ago it was 900 (!!!).

You can check current Prime (CPU) and Hash (GPU) difficulty here:
http://nexusoft.io/platform/Explorer