Mathmatics ques help needed?

2. The console on a piece of electronic equipment displays four flashing lights. These yellow, green, blue and orange lights flash on every 24 seconds, 27 seconds, 36 seconds and 45 seconds, respectively. All the lights instantaneously flash on when the equipment is started. On how many occasions during the first 3 hours of operation of the equipment will all the lights be on at the same time ?