First you need to subtract the two equations which becomes 2x+16=0
Now you move the 16 to the other side by subtracting 16 on both sides:
2x=-16
Now divide 2 on both sides to eliminate the 2 on 2x
x=-8
Now that you got -8 as x you can replace x on the two equations any one of them you only need to get one but I am going to use both of them to show you that it is the same: