A concert hall has 30 rows of seats with 20 seats in the 1st row, 22 seats in the 2nd row, 24 seats in the 3rd row, and so on. The price per ticket is $20. What is the dollar
amount collected by the box office if all the seats are sold for one concert?

sites:

i have not got your picture clearly so see it once again

answer: -10

step-by-step explanation:

s(t) = 1 - 10t

s(x) = 1 - 10x

s(x + h) = 1 - 10(x + h)

            = 1 - 10x - 10h

s(x + h) - s(x) = 1 - 10x - 10h - (1 - 10x)

                      = 1 - 10x - 10h - 1 + 10x

                      = -10h

= -10