The formula for DeltaH is DeltaHrxn = summation [nDeltaHf(products) - mDeltaHf(reactants)].
Note that DeltaH for products and reactants is taken to be at standard conditions.
m and n are numbers of moles.
Therefore, you will have DeltaHrxn=6(DeltaH C) + 3(DeltaH H2O) - 1(DeltaH C6H6) - 1.5(DeltaH O).
You can look up the standard enthalpies of the elements and compounds in a chemistry book.