First off, when using double quotes for strings, you don't need to concatenate them separately. Example:
$output = "<b>Name</b>: "."$name"."<p>"
/* could easily be */
$output = "<b>Name</b>: $name<p>"
Secondly, if you are trying to add the $_REQUEST variables in, don't use the echo statement.
if ($_REQUEST["Top40"] == "Top40") {echo "Top40<br>";};
/* should be */
if ($_REQUEST["Top40"] == "Top40") { $output .= "Top40<br>"; };
Anything to the right of .= will be appended to the variable on the left.