app\models\Invoice::getItemTaxable PHP Method

    public function getItemTaxable($invoiceItem, $invoiceTotal)
    {
        $total = $invoiceItem->qty * $invoiceItem->cost;
        if ($this->discount > 0) {
            if ($this->is_amount_discount) {
                $total -= $invoiceTotal ? $total / $invoiceTotal * $this->discount : 0;
            } else {
                $total *= (100 - $this->discount) / 100;
                $total = round($total, 2);
            }
        }
        return $total;
    }