`6.`

`a)2x+3=15`

`2x=12`

`x=6`

Vậy `x=6`

`b)28-3x=13`

`3x=15`

`x=5`

Vậy `x=5`

`c)(x-1954)*5=50`

`x-1954=10`

`x=1964`

Vậy `x=1964`

`d)30*(60-x)=30`

`60-x=1`

`x=59`

Vậy `x=59`

`7.`

`a)x+99:3=55`

`x+33=55`

`x=22`

Vậy `x=22`

`b)(x-25):15=20`

`x-25=20*15`

`x-25=300`

`x=325`

Vậy `x=325`

`c)(3x-15)*7=42`

`3x-15=6`

`3x=21`

`x=7`

Vậy `x=7`

`d)x(x+1)=2+4+6+...+2500`

`x(x+1)=1250*1251`

`x=1250`

Vậy `x=1250`

`e)(8x-16)(x-5)=0`

`8x-16=0` hoặc `x-5=0`

`8x=16` hoặc `x=5`

`x=2` hoặc `x=5`

Vậy `x in {2;5}`

`f)x-152:2=46`

`x-76=46`

`x=122`

Vậy `x=122`