This code checks if the original price is numeric before performing calculations to avoid the warnings.

   <?php
    // Original price
    $price = 5.16;

    // Percentage to add
    $percentage = 12;

    // Check if $price is numeric before performing calculations
    if (is_numeric($price)) {

        // Calculate newPrice with the percentage added and limit to 2 decimals
        $newPrice = round($price + ($price * $percentage / 100), 2);

        // Output the result
        echo "New Price: $newPrice";
    } else {
        // Handle the case where $price is not numeric
        echo "Invalid price value";
    }
    ?>