A book is 10 cm x 18 cm long and 2 cm thick. It has a protective paper ‘jacket’ over the entire cover and folding 5 cm under the front and back covers. How much paper is needed for the ‘jacket’?

Answer 1

so the paper needs to be 10+2+10 to cover the front, spine, and back.
Add 5+5 for the overlap

This assumes the book is 18cm high, not 10cm high.