can you please tell me the work behind of the 13.9% ROI? thanks

TABLE 2 VALUE OF A BACHELOR'S DEGREE TO WOMEN IN THE UNITED STATES, 2014 THROUGH 2016 Based on Mean Earnings of Full-Time, Year-Round Female Workers Costs (Ages 18-21): Net Tuition and Fees Foregone Earnings Total Costs Total Costs Discounted at 4 Percent Real Interest Benefits (Ages 22 to 65): Earnings for High School Graduates Earnings for Holders of a Bachelor's Degree Differential in Earnings Earnings Differential Discounted at 4 Percent Real Interest Net Present Value of a Bachelor's Degree (NPV) Return on Investment (ROI) $33,300 85,600 118,900 112,000 1,538,800 2,717,400 1,178,600 453,900 341,900 13.9%