Đáp án:
`a,`
`9x + 5 - (x + 20) = 4 (x + 20) + 2`
`⇔ 9x + 5 - x - 20 = 4x + 80 + 2`
`⇔ (9x - x) + (5 - 20) = 4x + (80 + 2)`
`⇔ 8x - 15 = 4x + 82`
`⇔ 8x - 4x = 15 + 82`
`⇔ (8 - 4)x = 97`
`⇔ 4x = 97`
`⇔ x = 97 ÷ 4`
`⇔ x =97/4`
`text{Vậy}` `x = 97/4`
`b,`
`5 (x - 6) = 20 (x - 5) + 2 (x + 30)`
`⇔ 5x - 30 = 20x - 100 + 2x + 60`
`⇔ 5x - 30 = (20x + 2x) + (-100 + 60)`
`⇔ 5x-30=22x - 40`
`⇔ 5x - 22x = 30 - 40`
`⇔ (5 - 22)x = -10`
`⇔ -17x = -10`
`⇔ x = -10 ÷ (-17)`
`⇔ x = 10/17`
`text{Vậy}` `x = 10/17`
