5. Решить уравнение: 21 + x = 48; 25 − 2x = 5; 144 : (3 + x) = 12.

1) \(21 + x = 48\).

\(x = 48 - 21 = 27\).

2) \(25 - 2x = 5\).

\(2x = 25 - 5 = 20\).

\(x = 20 : 2 = 10\).

3) \(144 : (3 + x) = 12\).

\(3 + x = 144 : 12 = 12\).

\(x = 12 - 3 = 9\).

Ответ: 27; 10; 9.