Multiplied the top line by 6
Got -6a+6b-6c=-30 correct?
added it to the second line and got
11b-4c=-21 (the a's canceled out)
multiplied that by -3 and got:
-33b + 12c = 63 (Is this right so far?) Because then you say to leave the first line intact (-a + b - c = -5) and write down the two lines left would it look something like...
-a + b - c = -5
11b - 4c = -21
-33b + 12c = 63
I'm not sure what this is supposed to look like as a final answer. I just followed your instructions the best I could