`7/5 - 57/36 xx (-6/19) + (-1/42) : 5/7`

`= 7/5 + 57/36 xx 6/19 - 1/42 xx 7/5`

`= 7/5 + 1/2 - 1/42xx 7/5`

`= 7/5 xx (1 - 1/42) +1/2`

`= 7/5 xx 41/42 + 1/2`

`= 287/210 + 105/210`

`= 392/210`

`= 196/105`

`4^n . 4^2 = 1024`

`4^(n + 2) = 4^5`

`n + 2 = 5`

`n = 5 - 2`

`n = 3 (` Thỏa mãn `)`