[
  "Draw a bar model: Let Sister's age 2 years ago = 1 unit. Then Maria = 3 units.",
  "Two years from now (4 years later): Sister = 1u + 4, Maria = 3u + 4. Sum = 4u + 8 = 32. So 4u = 24, 1u = 6.",
  "Maria now = 3 x 6 + 2 = 20. Answer: 20 years old."
]