The Radical King by Martin Luther King Jr is free on Audible via Alexa.
Typically $24.95 ($13.99 for Audible members), this book is free when you ask "Alexa, what’s free from Audible".
It will allow you to listen to the full book (11hrs, 8min) on an Alexa device.
I don’t see that you can use this to get it in the Audible app, still shows $13.99 for me and doesn’t show my reading status in the Audible app, appears to only be in Alexa.
https://www.audible.com/pd/The-Ra…rch_c3_lPr