How can you use a number line to compare and order numbers?

The numbers going to the left on a number line means the values are smaller and the numbers going to the right means the values are bigger. 

Take the value '0' for example, the value on the right of zero is '1', which is a value bigger than zero, and the value to the left of '0' is '-1', which is a value smaller than zero.

No solution : there is no number of boxes that she bought