Question

Architecture: In a 20-row theater, the number of seas in a row increase by three with each successive row. The first row has 18 seats:
a. Write an arithmetic series to represent the number of seats in the theater.
b. Find the total seating capacity of the theater
c. Front row tickets for a concert cost $60. After every 5 rows, the ticket price goes down by $5. What is the total amount of One generated by a full house?!

Would a look like 18+21+24....+7

Answer 1

i think it would look something like this:
\[t_n=18+3n\]

Answer 2

or i guess you could write:
{18+21+24+27+30+33+36+39+42+45+48+51+54+57+60+63+66+69+72+75}

or what you wrote, i guess:
{18+21+24....+75}