Đáp án + giải thích các bước giải:

`a)` `2x + 7 = 15`

`2x=15-7`

`2x=8`

`x=8:2`

`x=4`

Vậy `x=4`

`b)` `25-3(6-x) = 22`

`3(6-x)=25-22`

`3(6-x)=3`

`6-x=3:3`

`6-x=1`

`x=6-1`

`x=5`

Vậy `x=5`

`c)` `(25-2x)^3 : 5-3^2 = 4^2`

`(25-2x)^3 : 5-9 = 16`

`(25-2x)^3 : 5 = 16+9`

`(25-2x)^3 : 5 = 25`

`(25-2x)^3 = 25.5`

`(25-2x)^3 = 125`

`(25-2x)^3 = 5^3`

`25-2x= 5`

`2x=25-5`

`2x=20`

`x=20:2`

`x=10`

Vậy `x=10`

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