If a woman showing regular 28-day menstrual cycle ovulates on 12th of September, which of the following would be the next ‘safe period’ with regard to rhythm method of contraception?

Typically ovulation occurs on the 14th day of a 28-day menstrual cycle. Day 10 to 17 is the fertile period. The 18th day of one cycle to the 9th day of the next cycle would be the safe period.