Упростите выражение: 1) 4n-m/20mn² -3m+n/15m²n=? 2) b+3/9b-27 -b-1/b²-3b=?. 3) a+3/1-a•(a/a-3 + 3-a/a+3)=?

1) (4n - m) / 20mn² - (3m + n) / 15m²n = (3m * (4n - m) - 4n * (3m + n)) / 60m²n² = (12mn - 3m² - 12mn - 4n²) / 60m²n² = (-3m² - 4n²) / 60m²n² = - (3m² + 4n²) / 60m²n².

2) (b + 3) / (9b - 27) - (b - 1) / (b² - 3b) = (b + 3) / 9 * (b - 3) - (b - 1) / b * (b - 3) = (b * (b + 3) - 9 * (b - 1)) / 9b * (b - 3) = (b² + 3b - 9b + 9) / 9b * (b - 3) = (b² - 6b + 9) / 9b * (b - 3) = (b - 3)² / 9b * (b - 3) = (b - 3) / 9b.

3) (a + 3) / (1 - a) * (a / (a - 3) + (3 - a) / (a + 3)) = - 9 / (a - 3).