I used Michael Burnette's "Fast Track to Your Extra Class Ham Radio License". The new edition for the exam pool for 2020-2024 has just been released. This book is excellent, I studied for 6 days and passed. At this point, it is probably best to study for the new test, since there will be few or no opportunities for testing before July 1. As an aside, I went from not even thinking about amateur radio to an Extra in less than a month. It seemed best to get the exams out of the way and then explore the hobby. Lots of folks would disapprove of this method, but in the current testing environment it seems to have been a good decision. Another "no-code Extra" who is the ruination of this hobby? Not exactly, I am in month four of five straight months of CWOPS Morse code training. Everyone has a different way of doing things. A little more tolerance would do more for Amateur Radio than all the promotion in the world.