Why is the result 25?

Question

<?php$x = 5;$y = 6;

$paper = $x $x ;

$water = $y-- $x--;

echo $water $paper;

?>

I separately assigned the value first and then added, assigned the value first and then subtracted, added first and then assigned, and subtracted first and then assigned. Calculate them all separately and then add them up to calculate like this

Answer 1

paper=6 6;//After the end x=7

water=6 7;//After the end y=5, x=6