text_field value as a local variable in in-line template function


I'd like to conserve the sum total of several text fields on my form,
even as I set them to blank upon a user link action.

The following in-line snippet fails to store the value of my sum total
field locally for eventual reassignment. (I am re-assigning it because
the fields all have an observe_field nexus relating them, which
complicates things.)

<%= link_to_function "Itemize expenses" do |page|
                local_var = page[:operating_expense_admin_total].value
    page[:operating_expense_admin_other].value = ""
    page[:operating_expense_admin_advertising].value = ""
    page[:operating_expense_admin_management_fee].value = ""
                page[:operating_expense_admin_total].value = local_var
end %>

What is the proper way to extract values, store them locally and
reassign them , per the attempt above?