A fog horn sounds a blast for 2 seconds and then is silent for 8 seconds.
How many blasts are made in a 3 1/2 hour period?
2 second blast + 8 second pause= 1 blast every ten seconds
60 seconds in a minute= 6 blasts a minute
60 minutes in an hour = 360 blasts an hour
Then just multiply that by 3.5 and that is your answer