Ответ:

1) 2² + 8² = 4 + 64 = 68;
2) 7² - 4³ = 49 - 64 = -15;
3) 42² : 28 - 5² = 1764 : 28 - 25 = 63 - 25 = 38;
4) 42² : (28 - 5²) = 1764 : (28 - 25) = 1764 : 3 = 588.