Условие:

23 + (40 − 3);
(50 + 9) − 30;
69 + 7 + 1;
42 + 8 + 9;
20 + 14;
78 − 58.

23 + (40 − 3) = 40 + (23 − 3) = 40 + 20 = 60
 
(50 + 9) − 30 = (50 − 30) + 9 = 20 + 9 = 29
 
69 + 7 + 1 = 69 + 1 + 7 = 70 + 7 = 77
 
42 + 8 + 9 = 50 + 9 = 59
 
20 + 14 = (20 + 10) + 4 = 30 + 4 = 34
 
78 − 58 = (70 − 50) + (8 − 8) = 20 + 0 = 20