Abrams Company manufactured a wide variety of automobile parts, such as trucks, busses, and farm equipment. It has three major groups of parts: ignition parts, transmission parts, and engine parts. Abrams parts were sold both to original equipment manufacturers(OEMS) and to wholesalers. The wholesaler then resold the parts to retailers and retailers resold to consumers. This is called the aftermarket (AM).
comparing investment centers ROA using depreciate assets is tricky. Industrial division could have a higher ROA (as mentioned) if their equipment was older (lower book value)