law: The Central Goods and Services Tax Act, 2017
  8. Tax liability on composite and mixed supplies.-
  The tax liability on a composite or a mixed supply shall be determined in the following manner, namely:-
  (a) a composite supply comprising two or more supplies, one of which is a principal supply, shall be treated as a supply of such principal supply; and
  (b) a mixed supply comprising two or more supplies shall be treated as a supply of that particular supply which attracts the highest rate of tax.