awk usuage

can any1 guide me on simple awk to do extraction and calculation?
like for example if got data in 123.data how to i extract and sort the data giving my values like:
don,waiter,FnB,1500
mary,waitress,FnB,1500
alex,manager,hotel,2500
leo,ast manager,hotel,2000

how do i use this command to do a output like for example, under hotel what's the total wage as of the 4th field
which is alex's pay + leo's pay
and how do i do the amount of pay for FnB which is don's pay + mary's pay

appreciate the help. Cheers

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