Final answer:
The main purpose of the Interstate Commerce Act of 1887 was to prevent railroads from charging farmers and merchants high shipping rates.
Step-by-step explanation:
The main purpose of the Interstate Commerce Act of 1887 was to prevent railroads from charging farmers and merchants high shipping rates. The act required railroads to establish standard fares and publish these rates, which prevented discriminatory pricing practices against small farmers. This legislation was important for protecting the interests of farmers by ensuring fair and reasonable shipping rates.