mysql - Sum multiple times produced in a query (timediff)

Question

I have two fields:

• Initial (timestamp)
• Final (timestamp)

My query is:

SELECT TIMEDIFF(Final, Initial) 
    AS 'Worked Hours' 
    FROM `db_foo`
    WHERE matriculation='X' AND date='2017-yy-yy'

The result will be something like

Worked Hours    
03:34:00
02:34:00
01:00:00
[...]

Would it be possible to further sum those multiple timestamps, so to have the TOTAL amount of worked hours?

Example dataset (exported in csv):

DATE --- ID --- INITIAL --- FINAL --- MATRICULATION

2017-09-14,"29","2017-09-14 11:00:00","2017-09-14 14:34:00","4"
2017-09-14,"30","2017-09-14 17:00:00","2017-09-14 19:34:00","4"
2017-09-14,"31","2017-09-14 21:00:00","2017-09-14 22:00:00","4"

Desired output (it is the sum of the working times):

Worked Hours
07:08:00

Thanks in advance