How to combine data from 2 repositories

I have a question concerning combine datas from 2 repositorys in asp / mvc.

I have 2 repositories, for example, UserRepo and InvoiceRepo.

Now I want to create a query that contains user data and invoice data (for example: All users with address and data from the last invoice).

What is best way for doing this?

Why do you have to do it with one call?

var users = userRepos.GetUsers();
var lastInvoices = invoiceRepos.GetLastInvoiceForAllUsers();
var usersWithInvoices = (from x in users
                         select new UserWithInvoice(x, lastInvoices.First(inv => inv.userId = x.Id);

That will be two SELECTs and must be easier to understand.