If the topic is known: read 5 pages more every day than the day before, then:

Day 2: 20+5=25 (page)

Day 3: 25+5=30 (page)

Day 4: 30+5=35 (page)

Day 5: 35+5=40 (page)

Day 6: 40+5=45 (page)

A: Xiaohong read 35 pages in the fourth grade and 45 pages in the sixth grade.