3. 25 - (□ - 9) = 20 43 + (18 - □) = 52 □ - (15 - 6) = 69 28 - (12 + □) = 10

1. 25 - (x - 9) = 20 => x - 9 = 5 => x = 14.
2. 43 + (18 - x) = 52 => 18 - x = 9 => x = 9.
3. x - (15 - 6) = 69 => x - 9 = 69 => x = 78.
4. 28 - (12 + x) = 10 => 12 + x = 18 => x = 6.