it relates to after tax cash flow provided - and they ask for after tax nominal rate.
then they divide that by 1-t to get before tax nominal rate.
then add inflation.
If however the question provides you with an after tax cash flow need, and asks you for before tax nominal rate, your original solution - convert cash flow to “before tax nominal”, use that find before tax rate and then add inflation is the right approach. (You would use the 142,857 number).
If you have been given BEFORE TAX Salary & AFTER TAX cash flow requirement to be met from the portfolio with intention of leaving bequest (terminal value), you need to calculate the after tax return & adjust by tax 1/ (1-T) to get the before tax requirement (P. No 229 13 (ii)
However if you have been given AFTER TAX SAL & AFTER Tax Cashflow requirement, you need to adjust AFTER TAX cashflow to before tax 1 / (1-T) then calculate before tax requirement