HELP! Arithmetic/Geometric sequence questions, assignment due tomorrow

1. Write an expression, in simplified form, for the general term of the sequence in which the first term is 14 and each term is 5 less than the term preceding it.

2. In an arithmetic sequence, t15=-27 and t10=-12. Find the value of the fist term and the common difference.

3. Write an expression, in simplified form, for the general term of the sequence in which the first term is 16 and each succeeding term is 1/2 the before it.

Thank-you in advance.