5.86 Упростите выражение:

a) 0.4n - 0.7m - 0.9n + 0.7m = -0.5n; б) 6c - 8c - 4c + 21 - 13 = -6c + 8; г) 7/9x - 3/4x - 11/18x = (14 - 27 - 22)/36x = -35/36x; д) 0.3m - 2/7m - 3m + 6/7m = (0.3 - 3)m + (6/7 - 2/7)m = -2.7m + 4/7m = (-27/10 + 4/7)m = (-189 + 40)/70m = -149/70m; е) 1/7a + 3/4a + 1/4c = (4+21)/28a + 1/4c = 25/28a + 1/4c.