${r_3}{\mkern 1mu} {\mkern 1mu} = {\mkern 1mu} {\mkern 1mu} 0.529 \times \frac{{3 \times 3}}{3}{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} = {\mkern 1mu} {\mkern 1mu} 0.529 \times 3\mathop {{\text{ }}A}\limits^o {\mkern 1mu} = {\mkern 1mu} {\mkern 1mu} 1.587{\mkern 1mu} \mathop {{\text{ }}A}\limits^o $