ANSWER

8-10 year olds

a)    Page 55.

b)    150 pages.

Why a)    There is a secuence on the days that she read everyday: 10,  15,  22,   31,  42,  

We can see that the amount goes up by two: 5, 7, 9, 11. So the next increment is going to be 13. That is why the 6th day the increment is    42+13=55.

b)    Following the pattern, the increment would be: 5, 7, 9, 11,  13,  15,  17, 19,  21,  23 10,  15,  22,   31,  42,  55, 70, 87, 106. 127. 150.