Adding Fields In Tables

hi all

i can do simple additions in access but i have been asked to calculate fields in different tables

all i need to do is

i have 2 tables in my database
Table 1:main_database
Table 2:Security 2_3

and i have in table 1 got 1 field called Estimated security value
and in table 2 i have 2 fields called Sec 2 estimated value and Sec 3 estimated value

all i need to do is add all of the fields together in query or field in a form

i have tried =([Estimated security value]+[Security 2 & 3]![Sec 2 estimated value])+[Security 2 & 3]![Sec 3 estimated value]

but i get '#name error

thanks in advance
chris