We don't have to stress too much over the details, which are a little muddled here. When we scale the linear dimension by a factor of f we scale areas by a factor of [tex]f^2[/tex].
It's not totally clear from the question but let's say A is on the inner circle of radius r and B on the outer circle of radius R. The linear dimensions are scaled by the ratio [tex]R/r[/tex] so the area is scaled by
Answer: [tex] \dfrac{R^2}{r^2} [/tex]
