$\"\"$

The Drury Lane theater has $\"\"$ seats in the first row, hence $\"\"$ .

There are $\"\"$ row in all, hence $\"\"$ .

Each successive row contains one additional seat, hence $\"\"$ .

Hence the sequence is $\"\"$ .

The sum of the first $\"\"$ terms of an arithmetic sequence $\"\"$ .

The formula for $\"\"$ term: $\"\"$ .

$\"\"$

$\"\"$ .

Therefore, there are $\"\"$ seats in Drury Lane Theater.

$\"\"$

There are $\"\"$ seats in Drury Lane Theater.