Where did you get the value of 21 for Engineer? Intead of hardcoding it in your php, retrieve it from a table (job) in your database, where you might have something like this.
DROP TABLE IF EXISTS job;
CREATE TABLE job (
id int(10) unsigned NOT NULL AUTO_INCREMENT,
job varchar(20) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8;
/*Data for the table `job` */
insert into job(id,job)
values (1,'Manager')
,(2,'Owner')
,(3,'Director')
,(4,'Clerk')
,(5,'Engineer')
,(6,'Janitor')
,(7,'Worker')
,(8,'Jack of all trades')
;
Then you can add more job titles without changing your code. Just fill your option list for display with the result of a query on the job table. Save the value of the option in the "person" table, and join will tell you what job a person does.
Good luck,
Barry.