№3
1) \[(5.3 + a) - (a + 6.4) = 5.3 + a - a - 6.4 = -1.1\]
2) \[-(9.4 - b) + (-b + 3.7) = -9.4 + b - b + 3.7 = -5.7\]
3) \[-(x - 5.8 - y) - (11.3 - x) = -x + 5.8 + y - 11.3 + x = y - 5.5\]
4) \[-(a - b - 7.4) + (-7.4 + b + a) = -a + b + 7.4 - 7.4 + b + a = 2b\]
№4
1) \[(9.8 + k) - (3.4 + k) = 9.8 + k - 3.4 - k = 6.4\]
2) \[(-38 - m) - (12 - m) = -38 - m - 12 + m = -50\]