1. For each arithmetic series described below, write the series and calculate its sum. If it is not possible, explain why not. a. You know that the first term is 18, the last term is 72, and the common difference is 4.5. What is the series? What is the sum? b. You know that the series has nine terms and the last term is 18. What is the series? What is the sum? c. You know that the third term of an 18-term series is 29 and the terms are increasing by 10. What is the series? What is the sum?