To find a relative date 40 weeks in the past from September 16th, we need to deploy a simple manual calculation. First, convert 40 weeks to days by multiplying it by 7 (40 weeks * 7 days/week = 280 days). Then, subtract 280 days from September 16th. September 16th – 280 days = December 11th. Therefore, the relative date 40 weeks in the past from September 16th would be December 11th.