400 + 80 – 1 = 480 – 1 = 479
750 – 50 + 1 = 700 + 1 = 701
978 – 8 – 1 = 970 – 1 = 969
500 + 99 + 1 = 500 + 100 = 600
300 + 74 = 374
374 – 300 = 74
Ответ: 479; 701; 969; 600; 374; 74.