How to write the code for the back button?

Question

I have a php code here and I would like to create a "back" href to get me back to where I was before. Here\'s what I have:

Answer 1

Basically my code sends data to the next page like so:

**Referring Page**
$this = $_SERVER['PHP_SELF'];
echo "<a href='next_page.php?prev=$this'>Next Page</a>";

**Page with button**
$prev = $_GET['prev'];
echo "<a href='$prev'><button id='back'>Back</button></a>";