I dont see how it makes any difference to you. This is a pre-calculus question and I need help. I see that I am not getting it from you!

The first row has 7 seats, since k=0 zero when you are at the first row. If you move up to the second row k=1, so there are 7+2(1)=9 seats. If you move up to the third row k=2, so there are 7+2(2)=11 seats. You can continue this for k=3,...,24 (since there are 25 rows and we consider the first row to be row 0). The notation Plato posted tells you to add up each one of these terms. So,

\(\displaystyle \sum_{k=0}^{24}7+2k=7+9+11+13+...\), where \(\displaystyle k\) is the index of the summation, 0 is the lower bound (the initial value of k) and 24 is the upper bound (the final value of k). Thus, you begin at k=0 and add the following terms up until you get to k=24.

Hopefully that clears things up.