If you girls are not max using a N-Gacha and no other items give:

A) 1x N-girls chance 80%.
B) 1x R-girls chance 18.5%.
C) 1x SR-girls chance 1.5%.

If alle N-girls are max getting a N-Girl have around 1% of level a R-girl and 1% chance of leveling a SR-girl.

With all N-girls maxed N-Gacha give:
A) 1x N-wild chance 78%.
B) 1x R-girls chance 19.5%.
C) 1x SR-girls chance 2.5%.