How did the supreme court justify its ruling in the case of plessy v. ferguson?

Plessy v. Ferguson was a landmark decision of the U.S. Supreme Court issued in 1896. It upheld the constitutionality of racial segregation laws for public facilities as long as the segregated facilities were equal in quality – a doctrine that came to be known as "separate but equal"

letter d is correct.

congress also has implied powers, which derive from the necessary and proper clause of the constitution and permit congress "to make all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution in the government of the united states.