MVC :: Join 2 SQL Tables Together And Return Them In A Json?

I am new to MVC and am trying to join 2 SQL tables together and return them in a Json. One table is OutreachProgram. The other table is UserInfo. I want to return the rows from the OutreachProgram table that match on CenterID with the UserInfo table.

The code that exists now will pull all rows from the OutreachProgram table. I can't figure out how to add the UserInfo table to the query to make it work.

JsonGrid <OutreachProgram> grid =
new
JsonGrid<OutreachProgram>(db.OutreachProgram,
new
OutreachProgramFilter());
public Array GetItems(IQueryable<OutreachProgram>
source)
{ return (from r
in source.AsEnumerable()
select
new {
ID = r.OutreachProgramID, CenterID = r.CenterID, DateOutreachProvided = r.DateOutreachProvided.ToShortDateString(),
NameOfProvider = r.NameofProvider.ToString(),
}).ToArray();
}