vat and service tax on catering services

PRISM CATERERS Services provided Rs.27091 Add:Service Tax @ 5.15% Rs.1395 Total Rs.28486 Add:VAT @ 14.5% on 28486 Rs.4130 Grand Total Rs.32617 my doubt is 1.Criteria for charging both vat and service tax 2.why vat is charged on the amount including service tax.