In a triangle ABC, if $\mathrm{r}_1=3, \mathrm{r}_2=4, \mathrm{r}_3=6$, then $\mathrm{b}=$

• Correct answer
  A

  $2 \sqrt{6}$
• B

  $\frac{5 \sqrt{6}}{3}$
• C

  $\frac{7 \sqrt{6}}{3}$
• D

  $3 \sqrt{6}$

Hence, the correct answer is option: 'A'.