Answer:
1078
Step-by-step explanation:
Total no of rows (n) = 22
Since, 18, 20, 22 ..... forms an arithmetic sequence with first term (a) = 18 and common difference (d) = 2.
We need to find: Total no of seats in the theatre 
Formula to be used:
![S_{n}= \frac{n}{2}\bigg[2a+(n-1)d\bigg]](https://tex.z-dn.net/?f=S_%7Bn%7D%3D%20%5Cfrac%7Bn%7D%7B2%7D%5Cbigg%5B2a%2B%28n-1%29d%5Cbigg%5D)
Plug the values of a, d and n in the above formula, we find:
![\implies S_{22}= \frac{22}{2}\bigg[2(28)+(22-1)(2)\bigg]](https://tex.z-dn.net/?f=%5Cimplies%20S_%7B22%7D%3D%20%5Cfrac%7B22%7D%7B2%7D%5Cbigg%5B2%2828%29%2B%2822-1%29%282%29%5Cbigg%5D)
![\implies S_{22}=11[56+(21)(2)]](https://tex.z-dn.net/?f=%5Cimplies%20S_%7B22%7D%3D11%5B56%2B%2821%29%282%29%5D)
![\implies S_{22}=11[56+42]](https://tex.z-dn.net/?f=%5Cimplies%20S_%7B22%7D%3D11%5B56%2B42%5D)
![\implies S_{22}=11[98]](https://tex.z-dn.net/?f=%5Cimplies%20S_%7B22%7D%3D11%5B98%5D)

Thus, there are total 1078 seats in the theatre.