Since hours is a larger unit, there will be less hours than seconds. For example, if there are 120 seconds, how would you change this to minutes? Answer smaller to larger units means to divide by 60 since there are 60 seconds in a minute. 120 seconds would be 120/60 = 2 minutes.
Now, back to your problem. There are 60 seconds in a minute and 60 minutes in an hour, so there are 3600 seconds in 1 hour.
So to convert from seconds to hours, you'll have to divide by 3600.
x seconds = hours, so there are hours in x seconds.