Harold Reiter's "Building the Rings to Z6 and Z7"
Read this entire essay, paying special attention to understanding the operations ⊕ and ⊗ (read 'oplus' and 'otimes') in Z? and Z?. Then, work the problems 1 and 4 on Z??. You may check your solutions here.
Click https://s3.amazonaws.com/saylordotorg-resources/wwwresources/site/wp-content/uploads/2012/06/MA111_Z6and-Z7.pdf link to open resource.