destroy php variable

1<?php
2
3$first = 100;
4$second = 200;
5
6$third = $first + $second;
7echo "Sum = ".$third;
8// Destroy a variable with unset function
9unset($third);
10
11//after delete the variable call it again to test
12echo "Sum = ".$third;
13?>

1// Destroy a variable
2<?php
3unset ($var1, $var2.... )
4?>

11
2  75
3