Computer science: reference Theory of Computation cource

Problem: Implementing credit card machine to accept valid $16$ digits and reject invalid credit card digits

Pick four of the following ways to implement it: finite automata $($FA$),$ non$-$deterministic FA$,$ regular language, context$-$free grammar, pushdown automata, or Turing machine. You should have at least $5$ states in this problem and give at least $3$ of $5$ cases that your "machine" accepts.

$1-$ Describe the alphabet of this problem.

$2-$ Give a description of the states for this problem..

Give a description of the start and accept states for this problem.