3x^2+12x-2x-8-3(x^2-x+5x-5)=0

3x^2+12x-2x-8-3x^2+3x-15x+15=0

-2x+7=0

-2x=-7

x=3.5

1)(3х-2)*(х+4)=3х2+12х-2х-8=3х2+10х-8

2) 3*(х+5)*(х-1)= 3*(х2-х+5х-5)=3х2-3х+15х-15=3х2+12х-15

3) (3х2+10х-8) - (3х2+12х -15)=0

3х2+10х-8-3х2-12х+15=0

-2х=-7

х=3,5