Composition Functions

1. Define a function, f, to take an integer, n, from callers and
   return 2 * n + 1 to the callers.
2. Define another function, g, to take an integer, n, from callers and
   return 3 * n - 1 to the callers.
3. Define a main function to take user's number and call function f
   with user's number. Then, save the returning value from f and
   pass it to function g. Finally, print the returning value from g
   in a table where two column titles are x and g(f(x)).
4. Call main function.