The third term of an arithmetic series is 108 and the twelfth term is 54. Find
(a) the common difference of the series [4]
(b) the first term of the series [1]
The sum of the first n terms of the series is Sn .
(c) Find Sn . [3]
Given that Sn = 1200,
(d) Find the possible values of n.
you will be marked brainliest and get 15 points... plz URGENT

Luke started a weight-loss program. the first week, he lost x pounds. the second week, he lost pounds less than times the pounds he lost the first week. the third week, he lost 1 pound more than of the pounds he lost the first week. liam started a weight-loss program when luke did. the first week, he lost 1 pound less than times the pounds luke lost the first week. the second week, he lost 4 pounds less than times the pounds luke lost the first week. the third week, he lost pound more than times the pounds luke lost the first week.