Question 996890
Combined area of border and pond is  225+175=400 sq. meters.


Difference of radii of combined area and pond area is the width of the border.


{{{pi*r^2=A}}}
{{{r^2=A/pi}}}
{{{r=sqrt(A/pi)}}}


{{{highlight(sqrt(400/pi)-sqrt(225/pi))}}}


{{{5/sqrt(pi)}}}  OR   {{{5*sqrt(pi)/pi}}}