Ow to do reverse calculation in st & vat

How to calulate missing amount if VAT & service Tax both including? How should I do Reverse calculation if one item on which service tax chareged @ 12.36% & then on sub total (Item rate + Service tax) % VAT is charged. E.g. item base price is 417, ST on it is 52 & VAT is 23 = Total billing amount is 492. Suppose if I want to made this bill for Rs.450 Then how should I do reverse calculation? i.e How should I arrive at Item's base value if only final bill amount is known? I am using Tally software.