1.
brutto = 3500 zł
VAT = 23%
netto = x zł
123% --- 3500 zł
100% --- x zł
x = 2845,53 zł
2.
netto = 900 zł
VAT = 23%
brutto = x zł
100% --- 900 zł
123% --- x zł
x = 1107 zł
3.
brutto = 39000 zł
VAT = 23%
netto = x zł
123% --- 39000 zł
100% --- x zł
x = 31707,32 zł