The repeated chairs contribute \(4n\); only two end chairs are added to the entire line. The expression \(6n\) would add two end chairs for every table.

With one table both counts are \(6\). For any additional table, the actual total increases by \(4\), while \(6n\) increases by \(6\), so they no longer agree.

Answer

There are \(4n+2\) chairs. The expressions agree only when \(n=1\), when the number of tables is a positive integer.