A line with an undefined slope is a vertical line
the answer is: x=-6
Answer: I wrote the answer in docs so here is the pic for the whole equation i explained it too! I hope this helped
Hey there!

Your correct answer would be
. . .

Hope this helps.
~Jurgen
Multiply both sides by -3 to get rid of the negative and the fraction.
X - 3 = 21
Move the constants over to isolate the variable
X = 24