Tính

a) -3/7 + 5/13 + 4/7 + 8/13

b) 2/5 + 5/4 + (-2/5 + 5/4) - 5/2

c) 34/-13 . (1/3 - 5/6) : 17/26 + 1/2 . (1/5 - 3/4)
d) -5/4 : (-25/8) - 8/9 + 28/5 : -7