Answer:
3
Explanation:
Okay so 18 chairs were used more for 6 more rows so each row has 3 length.
x = 3
Now this makes no sense, because I don't know why you would leave 6 chairs if you only have 3 chairs for each row but....(Hue is weird so let's not question him)
Anyways mathematically
first arrangement = 2x + 6
second arrangement = 8x - 12
2x + 6 = 8x - 12
6x = 18
x = 3