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

And also this qn as well:D 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.

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