first, distribute the 6 to 1 + 3k
you then have -18 - 6k = 6 + 18k
then, add 18 to both sides, to cancel the -18 on the left
now it is 6k = 24 + 18k
after that, add -18k to both sides to cancel it on the right
this makes it -12k = 24
finally, divide both sides by -12, and k = -2.
