text: const MODERN_ACTIVITY = 15;
  const HALF_LIFE_PERIOD = 5730;
  
  module.exports = function dateSample(sampleActivity) {
    if (typeof sampleActivity !== "string") {
      return false;
    }
  
    let regexp = /^[0-9]/;
    if (!regexp.test(sampleActivity)) {
      return false;
    }
  
    sampleActivity = parseFloat(sampleActivity);
    if (sampleActivity <= 0 || sampleActivity > MODERN_ACTIVITY) {
      return false;
    }
  
    let k = 0.693 / HALF_LIFE_PERIOD;
    let time = Math.ceil(Math.log(15 / sampleActivity) / k);
    return time;
  };
  