[
  "Align decimal points. For the tenths column, regroup 1 one as 10 tenths since 0 < 1.",
  "9 = 8 ones + 10 tenths. 3.1 = 3 ones + 1 tenth. Ones: 8 - 3 = 5. Tenths: 10 - 1 = ?",
  "9 - 3.1 = 5.9. Answer: 5.9."
]