(Assuming it works at a constant rate)
45 minutes = 3/4 of an hour
If it works for 12 hours, it works for 12 : 3/4 = 16 times more than 45 minutes.
Since it works at a constant rate, it must also print 16 times more paper than in 45 minutes.
So, in 12 hours, the machine print 1500 x 16 = 24000 (papers)
