Could you tell me which one is right here in the following sentence?
Three hours ARE spent on this book. ------1
Or
Three hours IS spent on this book.----------2

Question

Answer

The plural - are - sounds better, obviously, as this fits with the plural of 'three hours'.

However, if you think of 'three hours' as a single block of time (as opposed to four hours, for example) , then the singular - is - may be possible.