sql - Getting the sum of a specific row -

i have maintenance table named ticket table , transaction table called workplan.

ticket table contains tickedid, ticketname, startdate,estimated time of completion , total number of hours columns.

and workplan table has workplanid, ticketid(foreignkey), currentdate , ticket name, no of hours, , hours remained columns.

for instance:

i have ticket entry shown below.

ticket id / ticket name  / start date    / estimated time of c.  /total number of hours  1           /sample name / 05.21.2013 /  05.23.2013             / 21hours   

and next table represents workplan.

workplanid  / ticket id / currentdate    / ticket name  / no of hours    / hours remained   1001       /1          / may.21.2013    /sample name     /3             /18  

...workplan id autogenerated.

if user manage his/her workplan. current date automatically derived. user input his/her no of hours.

my question how can difference between total number of hours ticket table , hours remained in workplan table?

so if user has managed workplan again next day,

workplanid  / ticket id / currentdate    / ticket name  / no of hours    / hours remained   1001       /1           / may.21.2013  /sample name /3                    /18     1002       /1           / may.22.2013  /sample name /4                    /14   

im using vb.net , sqlserver backend.

(binding source)

the lower value of hours_remained per ticket on last user update. so:

select total_number_of_hours - min(hours_remained)   workplan, ticket   ticket.ticket_id = workplan.ticket_id;