MATH PUZZLE: Can you replace...

My first job was working in an orange juice factory, but I got canned. I couldn't concentrate. Then I worked in the woods as a lumberjack, but I just couldn't hack it, so they gave me the axe. After that, I tried to be a tailor, but I just wasn't suited for it - mainly because it was a sew-sew job. Next, I tried working in a muffler factory, but that was too exhausting. Then, I tried to be a chef - figured it would add a little spice to my life, but I just didn't have the thyme. I attempted to be a deli worker, but any way I sliced it I couldn't cut the mustard. My best job was a musician, but eventually I found I wasn't noteworthy. I studied a long time to become a doctor, but I didn't have any patience. Next, was a job in a shoe factory. I tried but I just didn't fit in. I became a professional fisherman, but discovered that I couldn't live on my net income. I managed to get a good job working for a pool maintenance company, but the work was just too draining. So then I got a job in a workout center, but they said I wasn't fit for the job. After many years of trying to find steady work, I finally got a job as a historian - until I realized there was no future in it. My last job was working in Starbucks, but I had to quit because it was always the same old grind. So, I tried retirement and found that I'm perfect for the job!