Hello

ROI means return on investment, i.e, how many years it will take you to earn back what you paid for your degree. The amount you earn after this period is the return on your investment. Of course this is an idealised picture and the ROI can never be estimated with absolute accuracy. 

An example to calculate your ROI

(1)add the opportunity cost and the course tuition fees: 38 000 + 80 000 = 118 000

(2) Then subtract your previous salary from your post-MBA salary: 70 000 - 40 000 = 30 000

(3) Now divide 118 000 by 30 000: 118 000 ÷ 30 000 = 3.93

This calculation suggests that it would take you 3.93 years to earn back what you paid for your degree.