Their rates of work are : 

    A:    of the job per day;

    B:    of the job per day;

    C:    of the job per day.


If they completed the job in "t" days, then

    +  +  = 1,   or

    +  +  = 1,   or

    = 1,   which implies   = 1,  or  t =  days.


   
It means that A  made   =  part of the entire job,

              B  made   =  part of the entire job,   and

              C  made   =  part of the entire job.


Now notice that  242 = ,  so every  part of the job costs   = 15 rupees.


It means that  A should obtain  15*90 = 1350 rupees,

               B should obtain  15*80 = 1200 rupees,   and 

               C should obtain  15*72 = 1080 rupees.


Easy check:  1350 + 1200 + 1080 = 3630 rs.    ! Correct !