Answer:
Resulting equation is

Step-by-step explanation:
Isolate y in the first equation 
divide both sides by 3

Now we substitute this value of y into second equation


Hence the resulting equation is

Notice that question doesn't says to solve so there is no need to simplify or solve that equation further
Answer:
X=0
Step-by-step explanation:
most likely it's zero i also double checked it too so I think,you should be good.
Answer:
D
Step-by-step explanation:
y=4x+12
x=4y+12
x-12=4y
1/4x-3
Answer:
C; -21/10X + 23
Step-by-step explanation:
Combine like terms and simplify