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