How much work does gravity do on the book?
A 1.2 kg book is lying on a 0.70 m-hght table. you pick it up and place it on the bookshelf 2.2m above the floor.
How much work does your hand do on the book?
You do 1.2kg*9.8*1.5 = 17.6 J of work moving the book to the higher shelf.
That is the only source of work.
work of gravity = mass x gravitational const x change in height