Goal line on Bar Graph

[gatorfe]

I have a bar graph that shows me on time delivery % goal met on the y axis, months on the x axis, and in the body I am measuring two departments.  The OTD goal for both departments is 98% every month.  I am trying to add a line to the graph that shows me this 98% goal. The problem is that since I am measuring two departments it wants to show me two lines on top of each other for 98%.  Any suggestions on making this one line since I am measuring two departments within the graph?  I have attached a pic of the graph.  Thanks in advance.