We have the following:
We can see that the increase is constant, in each row it increases by 2, therefore the sequence would be as follows:
[tex]A(n)=18+2\cdot(n-1)[/tex]On the 12 row:
[tex]\begin{gathered} A(12)=18+2\cdot(12-1) \\ A(12)=18+22 \\ A(12)=40 \end{gathered}[/tex]That is, in row 12 there are a total of 40 seats
