Answer: the last option is the correct answer.
Explanation:
The given system of equations is expressed as
y = - 3x - 12- - - - - - - - - - - - -1
y = 3x + 24- - - - - - - -- - - - - - -2
We would apply the method of elimination. Since x has the same coefficient and the sign is opposite, we would eliminate x by adding equation 1 to equation 2. It becomes
y + y = - 3x + 3x - 12 + 24
2y = 12
Dividing the left hand side and the right hand side of the equation by 2, it becomes
2y/2 = 12/2
y = 6