To solve this problem you must apply the proccedure shown below:
1. The arithmetic sequence is:
[tex] an=a1+d(n-1) [/tex]
Where [tex] an [/tex] is the nth termn, [tex] a1 [/tex] is the first term, [tex] d [/tex] is the common difference between the terms and [tex] n [/tex] is the number of the term.
2. Based on the information given in the problem, you have:
[tex] a1=20\\ d=1\\ n=12 [/tex]
3. When you substitute these values into the formula, you obtain:
[tex] an_{12} =20+(12-1)\\ a_{12}=31 [/tex]
The answer is: [tex] 31 [/tex] seats
