Question 732603
{{{219.91=(pi)r^2 + 9(pi)r}}} --> {{{219.91/pi=r^2 + 9r}}} --> {{{70=r^2 + 9r}}} (rounding)
{{{70=r^2 + 9r}}} --> {{{r^2 + 9r-70=0}}} 
You can solve that quadratic equation easily by factoring:
{{{r^2 + 9r-70=0}}} --> {{{(r+14)(r-5)=0}}} --> {{{highlight(r=5)}}} because {{{r=-14}}} does not make sense.