Sub Articulo 92.0

 
 I wanna assign the equation numberings with some additional
 
 characters, i.e. like following
 
 --------------- equation ---------------  (1a)
 --------------- equation ---------------  (1b)
 --------------- equation ---------------  (1c)
 --------------- equation ---------------  (1d)
 
 some other comment.....
 
 --------------- equation ---------------  (2a)
 --------------- equation ---------------  (2b)
 --------------- equation ---------------  (2c)
 
 I know that LaTeX give the equation number with automatically increasing.
 How can I solve this problem?