to compute the path loss coefficient from data

Hi, i have to find the linear regression and ,most important thing, the slope of this curve in a logscale.In the x axis i have the distance and in the y the signal strength in dBm (4000 sampples for every distance).Now, to characterize this outdoor scenery,i need the best linear regression that describes in the best mode the trend of these samples and i need this parameter alpha (path loss coefficent).How is it possible? i hope that my question is clear because i do not speak, and so write, english well..i have attached the figure of the samples to understand better.Waiting the reply, thanks!