In the granger cases of the 1870s involving railroad regulation, supreme court decisions were significant because the decisions established that

1. racial segregation on transportation facilities is unconstitutional
2. government can regulate private business in the public interest
3. the regulation of business is solely a state government power
4. an end to the influence of the populist movement was near

In the Granger cases of the 1870s involving railroad regulation, Supreme Court decisions were significant because the decisions established that 

2. government can regulate private business in the public interest 

In response to the Supreme Court's 1886 ruling with regards to the Granger cases, Congress passed the Interstate Commerce Act of 1887. This act allowed federal regulations to be implemented on interstate lines.

10.4 is the answer for you