In the following script, which line(s) will cause an error(s)?

1 <?php
2       $count = 0;
3       $_xval = 5;
4       $_yval = 1.0;
5       $some_string = "Hello there!";
6       $some_string = "How are you?";
7       $will i work = 6;
8       $3blindmice = 3;
9 ?>