1) 2907 × 3 × 10 + 5403 = 8721 × 10 + 5403 = 87210 + 5403 = 92613
2) 780 × 5 × 100 – 20 471 = 3900 × 100 - 20 471 = 390000 - 20471 = 369529
Ответ: 2907 × 3 × 10 + 5 403 = 92613; 780 × 5 × 100 – 20 471 = 369529