If you would like to know how many words are on the list, you can calculate this using the following steps:
5/6 of the words on the list is 30 words
5/6 * x = 30 /*6
5 * x = 30 * 6 /5
x = 30 * 6 / 5
x = 36 words
Rafael needs to memorize 36 words on the vocabulary list for the German class.