A star twinkles every 9 minutes. A second star twinkles every 4 minutes. A third star twinkles every 15 minutes. If all the three stars twinkle at the same time at 4’ O clock in the morning, at what time did they all twinkle together last time before 4’ O clock in the morning?
1
1:00 a.m.
2
1:20 a.m.
3
2:20 a.m.
4
2:30 a.m.