Are my answers correct?

8. The first, second, and the nth terms of an arithmetic sequence are 2, 6, and 58 respectively,
i. Find the value of n

n = 15
ii. For that value of n, find the exact value of the sum of n terms.

S_15 = 450

3 answers

and this :
9. The second term of an arithmetic sequence is 7. The sum of the first 4 terms of the arithmetic sequence is 12. Find the first term a1, and the common difference, d, of the sequence.

answer: d = -8, a = 15
Your both answers are completely correct.
i got 3.998