What do you suggest to make the wages calculate

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PHP

Writing a php code, it's erroring out at over 40 hours. Have tried to correct but I can't find the issue. PLEASE HELP. I've submitted it already, just need to make that one correction to be regraded.

40 hours
    else if($hourly > 40){
        echo "Total pay is: ".(($hourly * $regular_pay)+ $hourly -40( * $overtime_pay) + $tips);
    }
}

//test the input data
function test_input($data) {
  $data = trim($data);
  $data = stripslashes($data);
  $data = htmlspecialchars($data);
  return $data;
}

?>

What I have tried:

I can't find the error, I've changed everything in the >40 hours code, but I still can't get it to calculate correctly. Any suggestions would be helpful.