Answer:
D.(2,-1,-1)
Explanation:
-a+4b+2c=-8
3a+b-4c=9
b = -1
Substitute b=-1 into the other equations
-a -4 +2c = -8
3a -1 -4c =9
Multiply the first equation by 2 so we can eliminate c
-2a -8 +4c = -16
Add this to the second equation
-2a -8 +4c = -16
3a -1 -4c =9
-----------------
a -9 = -7
Add 9 to each side
a-9+9 = -7+9
a =2
b=-1
Now we need to find c
-a +4b +2c = -8
-2 -4 +2c = -8
-6+2c = -8
Add 6 to each side
-6+6 +2c = -8+6
2c = -2
Divide by 2
2c/2 = -2/2
c=-1
(2,-1,-1)