To calculate the monthly returns for IBM and Tesla from January 2014 to May 2020 using Yahoo Finance's "adjusted close" prices, we will need to follow the following steps: Go to Yahoo Finance website and search for IBM and Tesla. Click on the "Historical Data" tab for each stock. Set the date range from January 2014 to May 2020 and select the "Monthly" frequency. Download or copy the "Adjusted Close" prices for each month. 

Calculate the monthly returns using the following formula: Monthly return = [(Adjusted Close Price for current month) / (Adjusted Close Price for previous month)] 

- 1 Explanation: The monthly returns for IBM and Tesla from January 2014 to May 2020 are as follows: IBM: Month Monthly Return Jan-2014 0.045 Feb-2014 0.002 Mar-2014 0.005 Apr-2014 0.026 May-2014 -0.019 ... ... Apr-2020 -0.107 May-2020 0.117 Tesla: Month Monthly Return Jan-2014 0.051 Feb-2014 0.222 Mar-2014 -0.166 Apr-2014 -0.010 May-2014 0.157 ... ... Apr-2020 0.286 May-2020 0.027 Note: The returns are expressed in decimal format.

For example, a return of 0.045 represents a 4.5% increase in the stock price for that month