Question 1077269
r will be close to 1/2 the length of each side (so the resulting circle just reaches the walkway).  Set {{{ r=15m }}} to do the calculation, but keep in mind r must be smaller than 15m in order for the pond not to actually reach the walkway.

{{{ 15m*2(pi) = 94.25m }}}  

{{{ highlight(94m) }}}