Cumulative goal line on Line Trend Chart

I have created a report formula query field to show my actuals in a cumulative way for my primary y axis. (It is grouped by week in the x axis.)  What would a query look like to create a goal line in the secondary y axis that shows an increase by 45 each week (goal is 45/week)?  I do not have a field to summarize the goal.  Is there another report formula query that could accomplish this?

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Colleen Burch
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