Receive a record not a tuple - plpgsql

Dear Friends

How can I call a function into a function? My problem is: I'm trying to calculate a tax(inss) over a employer salary. I created a function called inss that do it correctly, but when I create another one to show more attributes (inss is not a attribute, it is calculate over a salary) I receive a record (like {1,Mary,32.45} not a tuple. How can I solve it?

CREATE TABLE emp
(
  cod numeric
  name text NOT NULL,
  last_date timestamp,
  last_user text,
  salary numeric,
  CONSTRAINT pkey PRIMARY KEY (cod)
)

CREATE FUNCTION inss() RETURNS numeric AS '
SELECT salary*0.11 FROM emp;
'LANGUAGE 'sql';
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It is OK
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CREATE OR REPLACE FUNCTION mostra_inss() RETURNS setof record AS '

select name, inss(), salary from emp;

'LANGUAGE 'sql';
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--- Only for test --- DROP FUNCTION show_inss();
--- Only for test --- select inss();
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--- Another Test - Not OK

CREATE OR REPLACE FUNCTION show_inss() RETURNS VARCHAR AS '
DECLARE
inss float;
BEGIN
SELECT INTO inss inss() FROM emp;
RETURN inss;
END;
' LANGUAGE 'plpgsql';
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--- Another Test (NOT OK)
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create or replace function test_inss() returns record as '
      DECLARE
         d record;
      BEGIN
         for d in select name,salary,inss() from emp
         loop     
         end loop;
      RETURN;
   END;
   ' language 'plpgsql';

select test_inss();