Sửa đề
a) `15/7.8- 17/8.9 + 1/9.10 + 1/10.11`
`= (1/7 + 1/8) - (1/8 + 1/9) + 1/9 - 1/10 + 1/10 - 1/11`
`= 1/7 + 1/8 -1/8 - 1/9 + 1/9 - 1/10 + 1/10 - 1/11`
`= 1/7 - 1/11`
`= 4/77`
b) `2/3 x - 1/3 = 16x + 1/2`
`=> 2/3 x - 16x= 1/2 + 1/3`
`=> (2/3 - 16)x = 3/6 + 2/6`
`=> -46/3 x = 5/6`
`=> x = 5/6 : (-46/3)`
`=> x= 5/6 . (-3/46)`
`=> x=-5/92`
Vậy `x =-5/92`