5.9 Упростите выражение:

• a) $$x - (x - z) = x - x + z = z$$
• б) $$-(b - d) - d = -b + d - d = -b$$
• в) $$c - (a + c) = c - a - c = -a$$
• г) $$z + (y - x - z) = z + y - x - z = y - x$$
• д) $$a + (-b + c - d) = a - b + c - d$$
• e) $$-c - (n - c + r) = -c - n + c - r = -n - r$$
• ж) $$-(k - d) - (s + d) = -k + d - s - d = -k - s$$
• з) $$-(s + d) - (z + d) = -s - d - z - d = -s - z - 2d$$
• и) $$n - (c + n) - (-c - r) = n - c - n + c + r = r$$