Maria reads 36 chapters of a book in 9 hours.
What isТher rate in chapters per hour?

Step-by-step explanation:

the unit rate, in chapters per hour, would be how many chapters in one hour --- but, for 23 chapters/78 hours = this fraction (23/78) is already in simplified (i.e., reduced) form --- i.e., 23 is prime, and 78 = 2(39) = 2(3)13, so 23 and 78 contain no factors in common --- so, the unit rate would be (23/78) chapters per hour --- if the problem had been, for example, 23 chapters in 69 hours, then the unit rate would have been (23/69) chapters per hour = (1/3) chapters per hour, or one chapter every 3 hours (though this is not a unit rate)