excel - Calculate hours needed to balance account? -

i have accounts excel sheet input expenses, incomes (gst inclusive), , calculates how placed (e.g. -$717.75 month).

i gives gst content pay $taxableincome*3)/23 , rough guide how income tax should put away $taxableincome*0.17.

you tell program hourly rate is.

i wanting add program allow tell you need work x more hours month balance.

this wouldn't soo hard,

$deficit/$hourlyrate = hours needed work except each additional hour worked need add ($hourlyrate*3)/23 gst expense, , add $hourlyrate*0.17 income tax expense.

this part don't quite how work out.

so given hourly rate of $21.00+gst = $24.15/h , deficit of $717.75 how can work out how many more hours need work?

basically wondering how can formula of
    0 <= [(x1+x2+x3...)-(y1+y2+y3...)] / z1
x1 must increase until entire formula equals 0, x1 increases, must y1 , y2
x. = income source
y. = expense
z. = hourly rate (gst inclusive)

note while excel formula useful not expecting people work me, generic overview in pseudocode work.

so, set:

gross new wage incl. gst - new gst - new income tax) =                                  -(current income - current expense) or -(y-e)                                   -(y-e) >= 0  gross new wage - (gross new wage * 3/23) - (gross new wage * 0.17) = -(y-e)  gross new wage * (1 - 3/23 - 0.17) = -(y-e)  gross new wage = -(y-e) / (1 - 3/23 - 0.17)  new hours * gross wage rate (incl. gst) = -(y-e) / (1 - 3/23 -  0.17)  new hours = (-(y-e) / (1 - 3/23 - 0.17)) / gross wage rate 

that works, doesn't it?