Complex sentence: The 4000/8000 PETs were more explicitly targeted at professional/business use than the 2001/3000, which was the main purpose of the enhanced BASIC 4.0.
Split into simpler sentences: The 4000/8000 PETs were more explicitly targeted at professional/business use than the 2001/3000. Business customers were the main target for the features of the enhanced BASIC 4.0.