Calculate Revenue to meet a target margin

I know this is the kind of question that will leave me kicking myself, but i'm having a mind blank...

I want to know what i need to set my revenue at to hit a target margin (the target margin is a cell that will be editable).

The formula I came up with is


(Z13*(1+$AP$11))-'Pricing Data Original'!K13)/'Pricing Data Original'!K13)

Or

(Unit Cost*(1+Target Margin))-Current unit revenue)/'current unit revenue)

If I enter 50% as target margin it sets the revenue at 150% of Cost which = a margin of 33%, Setting the Target to 100% sets the revenue to 200% of the cost which equals a margin of 50%

Clearly what I've done is created a target profit not margin, but I can't work out how to convert it to a target margin.

any ideas

thanks