Question

I want answer of book exercise

Answer 1

Explanation:

Here is a solution with exercise package.

Its option answerdelayed allows you to print the answer where you want with \shipoutAnswer.

lastexercise means that if you don't put anything as answer reference, the Answer environment is referred to the previous exercise. However, I have also put \begin{Answer}[ref={...}], in this way you can move the code for the answers where you want, but you have to keep the order. For how I have created the code for the first answer of the chapter (to print CHAPTER ... in the final list), you also have to write it within the relative chapter.

Moreover, To have CHAPTER ... printed in the final answer list, you have to set \setboolean{firstanswerofthechapter}{true} at the beginning and \setboolean{firstanswerofthechapter}{false} at the end of the first answer of a chapter (maybe there's a smartest way to do it but it's above my level of knowledge).

Eventually, if you need horizontal lists you have to use tasks environment, otherwise the ordinary \Question is enough I put an example of both in my MWE.

Edit: I've changed the numbering as required by the OP in comment.

If you want the roman numbers begin from i. in the second question, just remove the [resume=true] option.

Second edit: To have the list of the second exercise correctly aligned, you have to use aligned instead of align*. Since these are systems, maybe it's better to put a curly bracket before, like here in Ex. 2.2: