getting notice message

“Notice: Undefined index: foo_x in C:wampwwwcoord.php on line 9
Notice: Undefined index: foo_y in C:wampwwwcoord.php on line 10″

here is my code :

<form action=” method=post>
<input type=”image” alt=’ Finding coordinates of an image’ src=”xy-coordinates.jpg”
name=”foo” style=cursor:crosshair;/>
</form>

<?Php

$foo_x=$_POST[‘foo_x’];
$foo_y=$_POST[‘foo_y’];

$m = $foo_x;
$n = $foo_y;

echo “(X,Y)=($m,$n) “;

?>

when i run this code am getting the above notice.
how to define the foo_x and foo_y variable ?
am new to php.
please help me.
thanks in advance !

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