As Laura’s mother rushed off to work, she quickly gave Laura some instructions. “If I don’t answer it means I’m in a meeting, but don’t worry, the meeting won’t last more than 30 minutes and I’ll call you back when it’s over.” Later that day, Laura needed her mother, but her mother was stuck in a meeting and couldn’t answer the phone. Laura concludes that she will have to wait no more than 30 minutes before she gets a call back from her mother. What law of logic did Laura use to draw this conclusion?