I'LL FIGURE IT OUT - WHAT?

I remember back in the 80's I used to carry a briefcase to work. Now one day I remembered a co-workers wandering eyes as I dialed the combination to unlock the briefcase. "Hey did you lose something" I said. He just looked at me and shook his head and said "it's only three numbers, I'll figure it out" What? A look of panic came over my face as this was a guy that did differential equations on his lunch break so if there was anybody that could figure it out it would be him. thankfully he never bothered with my briefcase cuz about the only thing in there was my lunch. HAHA!