8:26:12 hrs
8:27:12 hrs
7:12:34 hrs
9:12:30 hrs
B. 8:27:12 hrs
Interval of change = (L.C.M of 48,72,108)sec.=432sec.
So, the lights will again change simultaneously after every 432 seconds =7 min.12sec
Hence , next simultaneous change will take place at 8:27:12 hrs.