 Hello and welcome to this session. Let us understand the following question today. In an AP given L is equal to 28, S is equal to 144 and there are total 9 terms find A. Now let us write the solution. We know that sum of N terms that is S is equal to N by 2 multiplied by 2A plus N minus 1D. We can also write this as S is equal to N by 2 multiplied by A plus A plus N minus 1D. Now this is the Nth term so it can be written as S is equal to N by 2A plus AN. Now if there are only N terms in an AP then AN is equal to L where L is the last term so S is equal to N by 2A plus L where last term. Now, substituting the values of S and then L in this we get it implies 144 is equal to 9 by 2 multiplied by A plus 28. Now this implies taking 2 on this side we get 288 is equal to 9 multiplied by A plus 28. This implies 288 is equal to 9A minus 9A is equal to 288 minus 252. This implies 9A is equal to 36. This implies A is equal to 36 divided by 9 which gets cancelled by 4. It implies A is equal to 4. 12 to 4 is our required answer. I hope you understood the question. Bye and have a nice day.