*Help* Line of best fit across multiple Y axis line graph

Dear all, im struggling to plot a line of best fit for a cluster / multiple of Y axis line graph. Am wondering if this is doable through excel? The starting point of the the line is the first data point (all the line graph starts at the same point). Have attached a sample of what it should look like from an old research paper.

Any help / advice is greatly appreciated. Im using MS office 2010.