1 1/2 hours is the same as 1 hour and 30 mins.
In 1 hour there is 60 mins, so all together in 1 1/2 hours there are
60 + 30 mins = 90 mins
And since in 1 min there is 60 secs
So 90 mins = 90 x 60 secs = 5400 secs
So in 1 1/2 hours there are 5400 secs