A1.7 kg book is lying on a 0.77 m -high table. you pick it up and place it on a bookshelf 2.0 m above the floor. how much work does gravity do on the book?

You are given the mass of the book with an initial height of 0.77m. You are also given the final height of the book, 2m above the floor. The problem requires you to find the work done on the book. It is said that work is equal to force times distance. And that force is equal to mass times acceleration due to gravity.
W=Fd
W=mgd=mgh
W=(1.7kg)(9.8m/s^2)(2m-0.77m)
W=20.49J
The work is equal to 20.49J.