$3/a)2x+k=x-1$
$x_0=-2⇒2.(-2)+k=-2-1$
$⇔-4+k=-3$
$⇔k=1$
$b)(2x+1)(9x+2k)-5(x+2)=40$
$⇔18x^2+4kx+9x+2k-5x-10=40$
$⇔18x^2+4kx+2k+4x=50$
$x_0=2⇒18.2^2+4.2k+2k+4.2=50$
$⇔72+8k+2k+8=50$
$⇔10k=-30$
$⇔k=-3$
$c)2(2x+1)+18=3(x+2)(2x+k)$
$⇔4x+2+18=6x^2+3kx+12x+6k$
$⇔-6x^2-3kx-8x-6k=-20$
$x_0=1⇒-6.1^2-3k-8.1-6.1=-20$
$⇔3k-6-8-14=-20$
$⇔-3k=-2$
$⇔k=\dfrac{2}{3}$
$d)5(k+3x)(x+1)-4(1+2x)=80$
$⇔5kx+5k+15x^2+15x-4-8x=80$
$⇔5kx+5k+15x^2+7x=84$
$x_0=2⇒10k+5k+60+14=84$
$⇔15k=10$
$⇔k=\dfrac{2}{3}$