-1×1/7×(4/5+19/20)×(6×5/6+4×2/3)
= -1×1/7×(16/20+19/20)×(5+8/3)
= -1×1/7×(35/20)×(15/3)
= -1×1/7×(7/4)×(5)
= -1/1×1/4
= -1/4