turn Procedure into Function

Question

I’m trying to turn this procedure in function, to use inside another procedure, but I can’t evolve:

CREATE PROCEDURE bancodados.sp_calculo(param_id_cnpj varchar(14))
BEGIN
    SELECT id_cnpj, 
           AVG(valor)*12 AS fat, 
           regime, 
           aliquota,
           (aliquota*SUM(valor))/100 AS pagamento,
           fun_dia_pagamento(fun_data_pagamento(NOW())) 
    AS data FROM (
      SELECT
        a.valornf,
        a.id_cnpj,              
        b. regime,              
        c. minimo,
        c. maximo,
        c. aliquota             
      FROM  bancodados.tabela_valores a
        LEFT JOIN bancodados.tabela_empresa b
        ON a.id_cnpj = b.id_cnpj
        LEFT JOIN bancodados.tabela_anexos c
        ON b.regime = c.regime AND 
           a.valor >= c.minimo AND 
           a.valor <= c.maximo        
        WHERE (a.id_cnpj = param_id_cnpj AND 
        DATE_FORMAT(data_registro,'%Y-%m') < DATE_FORMAT(fun_mes_anterior(NOW()),'%Y-%m')
        AND 
        DATE_FORMAT(data_registro,'%Y-%m') >= DATE_FORMAT(fun_12meses_antes(NOW()),'%Y-%m')
    ))x;
END $$