Calculated fields in Laravel using Query Builder

I've been working in a Laravel Project and I want to know how can I show a calculated field in a blade view? I want to retrieve some information from an invoice and a Total calculated field.

I would like to get this result, but using Eloquent ORM. The query is this:

SELECT 
    invoiceheader.id, 
    invoiceheader.customerlastname,
    invoiceheader.customerfirstname, 
    invoiceheader.customernit,
    invoicedetail.productid, 
    invoicedetail.quantity,
    invoicedetail.saleprice, 
    (quantity * saleprice) as Total
FROM invoiceheader 
INNER JOIN invoicedetail
    ON invoiceheader.id = invoicedetail.invoiceid

Thank you so much in advance.

via krlosfgx