Megan read an average (mean) of 2 books a day for 4 days. How many books will Megan need to read on days five and six so that she can say that she read an average of 3 books a day over 6 days?
3 * 6 = 18
2 * 4 = 8
18 - 8 = 10
10 / 2 = 5 books a day on days 5 and 6.