Help with a maths problem?

To keep my discount card for life i have to leave my job when my age + number of years of service add up to 80. i know its not rocket science but i cant work it out. my age is 37 and i have 6 years service. so how blokey more years do i have to work to keep my card. hope that makes sense.thanks could you do me a favour and tell me how you worked that out please. i did come up with roughly the same but i wasnt sure if i was right.
Answer
Today your age is 37 & you have done 6 years of service.37+6=43.you fall short by 80-43=37 years.since as you grow older, the length of service also goes up by same amount. so you will require 37/2=18.5 years from here to fullfil the requirement.after 22 years, you would be 37+18.5=55.5length of service would be 6+18.5=24.5which add up to 55.5+24.5=80ans. 18.5 years from now.