Please teach me how to do qn 8 and 9. Qns 8 and 9 are attached.

And also this qn as well Thks alot!!

Qn 3) The sum of the first 3 terms and that of the last 3 terms of an AP 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.

Note:For better view, pls double click and zoom in.thks