成套 is a separable verb (离合词) meaning 'to form a complete set' or 'to be sold as a set'. It often describes products, furniture, equipment, or documents that come as a coordinated group. When you need to insert a numeral or measure word, the verb splits: 成 + number + 套, e.g. 成三套 ('form three sets'). The object usually follows the whole verb or appears between the syllables.