Tbf.. Most people doing upwards of 20+ hours are probably doing most of it reading around subjects. Unless the uni goes crazy on examinations. Or doing courses like Med.
Very subjective as it depends how quickly you read and write essays for my subject. I'd say I average around 25; 5 on lectures, 3 on classes, 2 on tutes, 10 on reading, 5 on essay writing. But the reading and essay writing can easily increase to 25 total