Add two values in pdf invoice

Hello everyone,

I just want two add two variable in my pdf invoice template.

$line1 = ((string)$item['line_total']); //return $11.75												 
 $line2 = ((string)$item['line_tax']); // return $1.75
 $x = ((string)str_replace(get_woocommerce_currency_symbol(),'',$line1)); // remove $ sign from $line1
 $y = ((string)str_replace(get_woocommerce_currency_symbol(),'',$line2)); // remove $ sign from $line2
echo $x + $y;

// add $x and $y values But it return “0”

plz help me to solve this plz