(i) Define an arithmetic progression (AP) and the term "common difference".
(ii) The sequence 3, 7, 11, 15, … is displayed on a notice board. Without carrying out any algebraic calculation, give two distinct reasons to justify that this sequence is an arithmetic progression.
(iii) The next term of the sequence has been accidentally erased. Describe the reasoning you would follow to predict the missing term and state its value.