Answer
$$1110 \ seats$$
Work Step by Step
We know the following series to represent the given situation:
$$\sum _{i=2}^{20}\:\left(a_{i-1}+3\right)$$
Where $a_1$ is equal to 2, since this is the number of seats in the first row. Simplifying, we find the total number of rows is:
$$1110 \ seats$$
