Условие:

35 + 823;
74 + 731;
50 − (34 + 9);
50349;
8 + 6 + 12 + 4;
9 + 7 + 13 + 11.

35 + 823 = 4323 = 20;
74 + 731 = 8131 = 50;
50 − (34 + 9) = 5043 = 7;
50349 = 169 = 7;
8 + 6 + 12 + 4 = (8 + 12) + (6 + 4) = 20 + 10 = 30;
9 + 7 + 13 + 11 = (9 + 11) + (7 + 13) = 20 + 20 = 40.