Номер 42

30 · 2 = 60;
3 · 80 = 240;
60 : 3 = 20;
60 : 30 = 2;
100 : 2 = 50;
100 : 20 = 5;
(20 + 80) : 4 = 25;
80 – 20 : 4 = 75.