What is the sum of the arithmetic series below? -110 + -100 + -90 + -80 + + -10 + 0 + 10 + + 80 + 90 + 100 + 110?

Problem 3 a bank charges a service fee of $7.50 per month for a checking account. a bank account has $85.00. if no money is deposited or withdrawn except the service charge, how many months until the account balance is negative