This was very cool, I really enjoyed it. Most of the puzzles were very clever, I really liked: 11 - Negative and 6 - Titanic. I could not figure out 12-Minefield (so I skipped it). The last puzzle was a bit strange (I think maybe 1M would have been better than "∞"). It reminded me of being in math class (and it's been years... I've missed math class). Good job, I had a lot of fun playing this.