Help with sum function

[WinDancer]

I want to update the [Total Employees] field in the tbllassSurvey table to the sum of the different employees by type of work they do [1d]+[2d].

here is my code:
UPDATE tblClassSurvey SET tblClassSurvey.[Total Employees] = Sum([1d]+[2d]);

Running the query returns error 3122 'You tried to execute a query that does not include the specified expression "Total Employees" as part of an aggregate function'.

Help, please?

 

[boblarson]

It would be:

UPDATE tblClassSurvey SET tblClassSurvey.[Total Employees] = ([1d]+[2d]);