How Many Times Do You Laugh

Jane laughs at a joke once when you tell it. Fred laughs at a joke twice. Once when you tell it and once with you explain it to him. Susie laughs at a joke three times. Once when you tell it, once when you explain it to her, and once when she understands it. Mark laughs at a joke twice. Once when you tell it and once when you explain it to him. He never understands it. Will laughs at a joke once when you tell it. There's no use trying to explain it to him.