Đáp án:

`(x-3)/20 + (x+7)/30 + (x+19)/42 + (x+33)/56+(x+49)/72+(x+67)/90 = 306`

`(x-3)/20-1 + (x+7)/30-1 + (x+19)/42-1 + (x+33)/56-1+(x+49)/72-1+(x+67)/90-1 = 306-6`

`(x-23)/20 + (x-23)/30 + (x-23)/42 + (x-23)/56+(x-23)/72+(x-23)/90 = 300`

`(x-23)*(1/20 + 1/30 + 1/42 + 1/56+1/72+1/90) = 300`

Đặt `A = 1/20 + 1/30 + 1/42 + 1/56+1/72+1/90`

`=>` `A = 1/(4*5) + 1/(5*6) + 1/(6*7) + 1/(7*8)+1/(8*9)+1/(9*10)`

`=>` `A = 1/4-1/5 + 1/5-1/6 + 1/6-1/7 + 1/7-1/8+1/8-1/9+1/9-1/10`

`=>` `A = 1/4-1/10`

`=>` `A = 6/40`

`=>` `A = 3/20`

`=>` `(x-23)*3/20=300`

        `x-23=300:3/20`

        `x-23=300*20/3`

        `x-23=2000`

        `x=2023`

Vậy `x=2023`