[
  "When the tenths in the first number are too small to subtract, regroup 1 one as 10 tenths.",
  "4.5 = 3 ones + 15 tenths. 3.6 = 3 ones + 6 tenths. Ones: 3 - 3 = 0. Tenths: 15 - 6 = ?",
  "4.5 - 3.6 = 0.9. Answer: 0.9."
]