英文数列题目 In a particular arichmetic progression,the sum of the

英文数列题目 In a particular arichmetic progression,the sum of the 9th and 10th terms is-64.Also
In a particular arichmetic progression,the sum of the 9th and 10th terms is-64.Also,the difference between the sum of the first 5 terms and 2 times the fifth term is-49.What is the sum of the first 30 terms?