labour cost calculataion problem

hi in kaplan ma1 book i have come across an example and a part of it does not make sense to me . please could some1 explain what m i missing here. thanks department m payment to employees=15000 income tax=5000 employees benefit contribution =3400 employers benefit contribution=4000 hence gross wage =23400 it is also stated that net pay is simply the payment to employees =15000 now here is the confusion it calculates the total labour cost for department M as gross pay=15000 ?? employers benefit contribution=4000 total labour cost =19,000 why does gross pay equal 15,000 here but above calculated as 23400 . it is mentioned at the end that income tax and employees benefit contribution have already been deducted from gross pay so already has been accounted for . can someone please explain what m i missing here . its from chapter 6 ma1 kaplan book page 97 thanks