Arithmetic Progression X.x

Thank you for helping! I am soooooooo frustrated with arithmetic and geometric progression because I keep getting stuck at it. sigh.

Q1: The sum to n terms of a particular series is given by Sn = 17n - 3(n^2). Show that the series is an arithmetic progression and state the value of it's common difference.

Q2: The sum of the frist 3 terms and that of the last three terms of an arithmetic progression are 9 and 57 respectively. It is known that the sum of the whole sequence is 121. Find the number of terms in this sequence.

Thank you!