Упростите выражение: 1) -1,6x * (-5y); 2) -7a - 9b + a + 11b; 3) a - (a - 8) + (12 + a); 4) -3(c - 5) + 6(c + 3).

1) $$-1.6x \cdot (-5y) = 8xy$$ 2) $$-7a - 9b + a + 11b = -6a + 2b$$ 3) $$a - (a - 8) + (12 + a) = a - a + 8 + 12 + a = a + 20$$ 4) $$-3(c - 5) + 6(c + 3) = -3c + 15 + 6c + 18 = 3c + 33$$