Answer:
Found several answers to your question so I thought I'd give you a few to choose from or make up your own answer from them :)
"The judicial Power of the United States, shall be vested in one supreme Court, and in such inferior Courts as the Congress may from time to time ordain and establish."
"It is up to Congress to decide what other federal courts we will have. But one of the first things Congress did in 1789, the year the new government got going, was to set up a federal judiciary, including the Supreme Court—with six Justices."
Good luck! Hope this helped :)
