What is the solution of the system? use substitution. y=x+6y=2x

a. (6,12)
b. (-12,-6)
c. (-6,-12)
d. (2,4)

im very confused so explain to me how to get to the answer.

What the question means by substitution is that you will take each answer and put it into the original equation. Lets start with a.

a. (6,12): the first number will always be x, so anywhere you see an x in the original equation, put a 6. The second number will always be y, so anywhere you see a y put a 12.
y=x+6y=2x
(12)=(6)+6(12)=2(6)
Does this make sense? Not quite.

b. (-12,-6)
(-6)=(-12)+6(-6)=2(-12)
Does this make sense? No

c. (-6,-12)
(-12)=(-6)+6(-12)=2(-6)
Does this make sense? No

d. (2,4)
(4)=(2)+6(4)=2(2)
Does this make sense? Not just quite.

It seems like it is either A or D but the math says that it is not either of them.