How to avoid reverse engineering of an APK file?

Question

I am developing a payment processing app for Android, and I want to prevent a hacker from accessing any resources, assets or source code from the APK file.<

Answer 1

 1. How can I completely avoid reverse engineering of an Android APK? Is this possible?

Impossible

 2. How can I protect all the app's resources, assets and source code so that hackers can't hack the APK file in any way?

Impossible

 3. Is there a way to make hacking more tough or even impossible? What more can I do to protect the source code in my APK file?

More tough - possible, but in fact it will be more tough mostly for the average user, who is just googling for hacking guides. If somebody really wants to hack your app - it will be hacked, sooner or later.