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

Решим уравнения: 1) 25 – (x – 9) = 20 x – 9 = 25 – 20 x – 9 = 5 x = 5 + 9 x = 14 2) 43 + (18 – x) = 52 18 – x = 52 – 43 18 – x = 9 x = 18 – 9 x = 9 3) x – (15 – 6) = 69 x – 9 = 69 x = 69 + 9 x = 78 4) 28 – (12 + x) = 10 12 + x = 28 – 10 12 + x = 18 x = 18 – 12 x = 6