Get A SUM Of The Items In My Grouped Query?

I have a list of postcodes in a query (ThisInstructorsPostcodes) and another query that pulls back sales referrals (LastWeeksReferrals)I am using the below syntax to perform the linq equivalent of LEFT OUTER JOIN so I always get a postcode back, even if there were no referrals for it.

dim final = from tip in ThisInstructorsPostcodes _
group join lwr in LastWeeksReferrals on tip.PostcodeID equals lwr.PostcodeID Into lwrgrp = group _
from lwrgrpq in lwrgrp.DefaultIfEmpty _[code].....

The results I am getting are so close to what I need, but I am getting a bunch of InstructorReferrals objects in the lwrgrpq column and what I want to do is simple sum of the all the 'Referrals' integers in those InstructorReferrals objects.I thought this would work:

dim final = from tip in ThisInstructorsPostcodes _
group join lwr in LastWeeksReferrals on tip.PostcodeID equals lwr.PostcodeID Into lwrgrp = group _
from lwrgrpq in lwrgrp.DefaultIfEmpty _
select new with {tip.AreaDistrict, lwrgrpq.Sum(function(x) x.Referrals) }

...but it doesn't - fails with the error: Anonymous type member name can be inferred only from a simple or qualified name with no arguments.I have only used this linq query structure in order to mimic the outer join behaviour of sql, does anyone know how I can fix this so that my grouped items are not anonymous types?