Đáp án:

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`16,`

`(-5)/7 (2/5 - x) - 1/3 = 1/5 - 3/10`

`↔ (-2)/7 + 5/7x - 1/3 = (-1)/10`

`↔ 5/7x + ( (-2)/7 - 1/3) = (-1)/10`

`↔ 5/7x - 13/21 = (-1)/10`

`↔ 5/7x = (-1)/10 + 13/21`

`↔ 5/7x = 109/210`

`↔ x = 109/210 ÷ 5/7`

`↔ x = 109/150`

Vậy `x=109/150`

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`17,`

`5/3 (-6/5 + x) - 1/4 (2/3 - 1) = (-3)/8`

`↔ -2 + 5/3x - 1/4 × (-1)/3 = (-3)/8`

`↔ -2 + 5/3x - (-1)/12 = (-3)/8`

`↔ 5/3x + (-2 - (-1)/12) = (-3)/8`

`↔ 5/3x - 23/12 = (-3)/8`

`↔ 5/3x = (-3)/8 + 23/12`

`↔ 5/3x = 37/24`

`↔ x = 37/24 ÷ 5/3`

`↔ x = 37/40`

Vậy `x=37/40`

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`18,`

`(-3)/4 × (8/9 - x) + 3/8 = (-2)/3 × 1/2`

`↔ (-3)/4 × (8/9 - x) + 3/8 = (-1)/3`

`↔ (-3)/4 × (8/9 - x) = (-1)/3 - 3/8`

`↔ (-3)/4 × (8/9 - x) = (-17)/24`

`↔ 8/9 - x = (-17)/24 ÷ (-3)/4`

`↔ 8/9 - x = 17/18`

`↔ x = 8/9 - 17/18`

`↔ x = (-1)/18`

Vậy `x=(-1)/18`

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`19,`

`2/3 (x - 9/4) = 3/7 (7 - 1/6) - 1/3`

`↔ 2/3 (x - 9/4) = 3/7 × 41/6 - 1/3`

`↔ 2/3 (x - 9/4) = 41/14 - 1/3`

`↔ 2/3 (x - 9/4) = 109/42`

`↔ x - 9/4 = 109/42 ÷ 2/3`

`↔ x - 9/4 = 109/28`

`↔ x = 109/28 + 9/4`

`↔ x = 43/7`

Vậy `x=43/7`

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`20,`

`4 - 2/3 (x - 3) = 2 - 1/2 + 2/3`

`↔ 4 - 2/3 (x - 3) = 3/2 + 2/3`

`↔ 4 - 2/3 (x-  3) = 13/6`

`↔ 2/3 (x-3) = 4 - 13/6`

`↔ 2/3 (x-3) = 11/6`

`↔ x-  3 = 11/6 ÷ 2/3`

`↔ x - 3 = 11/4`

`↔ x = 11/4 + 3`

`↔ x = 23/4`

Vậy `x=23/4`