Line Chart need an Extra trend line

[techvarun]

Hi All

I have a Line chart with actual and budget as expressions and day of the month as Dimention.

Now my requirement is i need to draw a third static line called trend

and the requirement if i have date till 15 th  and my trend value is 55.25 i need to draw a straight line from day 15 till end of the month

Please suggest someways to acheive the above

Thanks

Varun