Assistance with a few algebraic series and sequences questions please

Struggling with three math questions, much obliged if any assistance can be given.

1. Determine the values of x for the following arithmetic sequence. Give an an algebraic solution.

2. Find the sum of the first 15 terms of an arithmetic series if the middle term is 92. Give an algebraic solution.

3. Find the general term(s) of a series if the second term is 15 and the sum of the first three terms is 93. Give an algebraic solution and write the first four terms.

Thanks for any help that can be given.

Dan.