Compare Values In Multiple Text Boxes

I've a page where I'm calling record from Database. Each record has an
ID and a text box displayed on the page. When the user fills in the
values of a text box, depending on the values of the text box i've to
do some further work. For eg. I've to add two records if the textbox
value of 2 records is same.

I'll try to create an example here
<-----this is from the DB-------> <-----this is form field--->
ID Task Hrs text box
1 adsfsd 1 a <---- user fills this
2 asdf 1.5 b <---- user fills this
3 eyst 2 a <---- user fills this
4 dghjfghj 2 c <---- user fills this
5 xdfb 1 b <---- user fills this
6 tyety 1.5 c <---- user fills this
________
| Submit |
--------------

So the user has to add hrs of those boxes for which have same values
entered by user. such as adding hrs of record 1 and 3 since both have
"a" entered by the user, adding record 2 and 5, as both have "b"
entered by the user and so on and so forth.