Addition of Two Numbers in PHP

After writing a  hello world  program, I will make a  program that will show that how to add two numbers in PHP, which is very important for beginners to learn PHP.
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<?php
$a=10;                            //Assign 10 to  variable a
$b=15;                         // Assign 15 to  variable b
$c=$a+$b;                   // Add a and b and assigns to c
echo $c;                         // Print c
?>
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Otput: 25

You can check this program using online PHP interpreter.
Link-http://www.runphponline.com/

To know how was it executed, see the video.