Creating MYSQL trigger

I need a trigger written for my mysql database. I need the trigger for the following: when I add time to my die_makers table, it will add the time to the time already in the main table, so I will need a sum. So if prod_jobs.job_time already has 45 min, and I add a entry to die_makers.job_time lets say 10, then prod_jobs.job_time will automatically change to 55m.