determine the AP whose fourth term is 18 and the difference of ninth term from the fifteenth term is 30. plz explain with statement. It is given that 4th term is 18. a4= 18 a + 3d = 18 a = 18 - 3d ... (1) Also, a15- a9= a+14d - 1 - 8d = 30 6d = 30 d = 5 Thus, from (1), we get, a = 18 - 15 = 3 Therefore, the AP is: 3,8,13,18,23 ...... here how do we get Also, a15- a9= a+14d - 1 - 8d = 30 6d = 30 d = 5 Thus, from (1), we get, a = 18 - 15 = 3