Explanation:
the 60 preliminary published articles are a constant.
all the new articles are simply added to that to get the total number of published articles.
every months produces 12 more articles.
so,
m = 1 means a = 60 + 1×12 = 72
m = 3 means a = 60 + 3×12 = 60 + 36 = 96
m = 4 means a = 60 + 4×12 = 60 + 48 = 108
m = 9 means a = 60 + 9×12 = 60 + 108 = 168