Electricity bill charges - Energy Australia

How they compute the charges of the electricity bill:

This reading - Last Reading = Energy used x Usage split x rate  = cost
Plus Elec SAC
Plus 10% GST

Example:
34252 - 33039 = 1,213kWh x 15.6c = $189.23

Electricity Service Availability Charge (SAC)
Days covered x Rate
85                     x 39.00c  / day  = $33.15

====

$189.23
+

$33.15
----------
$222.38
+

$ 22.23 (10% GST)
----------
$244.68  (85 days elec bill)

Rates: Energy Australia
15.60 cents per kWh
39.00 cents per day (SAC)