34%

the elkins act and the hepburn act regulated railroads by

outlawing kickbacks to the smallest companies and setting higher railroad rates.

outlawing rebates to the largest customers and setting railroad rates.

outlawing tax breaks to the largest railroads and changing railroad rates.

outlawing tax breaks to the smallest companies and raising railroad rates.

outlawing rebates to the largest customers and setting railroad rates.

Explanation:

Railroads were the dominant force in shipping of items from rural areas. Farmers and other small shippers were charged high freight fees at that time. Businesses that were shipping more items were offered rebates and these undue practices led to the creation of Interstate Commerce Commission (ICC).  

ICC were put in place to reduce the bad practices by the railroads but they were not effective in discharging their duties as expected and that prompted the 32nd President of the United States of America, President Roosevelt, to ask the congress to alter the ICC act. The amendment was named Elkins Anti-Rebate Act (1903) and they banned the rebate practices by the railroads to high-volume shippers.