1) 100 * x = 4000
x = 4000 : 100
x = 40
Проверка:
100 * 40 = 4000
2) x * 5 = 125 * 4
x * 5 = 500
x = 500 : 5
x = 100
100 * 5 = 125 * 4
500 = 500
Ответ: 1) x = 40; 2) x = 100.