Z-value using Z-table or t-table.

Hi there. I don't really understand how the solution to the following came about:

http://i30.tinypic.com/t8qefm.jpg

The answers after dictate: "To find where this value comes from, look up 0.49 backwards on the Z table, or look up for degrees of freedom the table."

Firstly, I don't understand why I'm supposed to look up 0.49 on the Z table and not 0.01? I'm also confused as to how to use the table 'backwards', especially if/when interpolation comes into it.

Secondly, why does the degree of freedom = ?