Answer
$6.72\times 10^6m$
Work Step by Step
We know that
$I=(\frac{r_1}{r_{\circ}})^2 10^{\frac{\beta}{10dB}}$
This simplifies to:
$r_{\circ}=r_110^{\frac{\beta}{20dB}}$
We plug in the known values to obtain:
$r_{\circ}=(3.0m)10^{\frac{127dB}{20}}$
$\implies r_{\circ}=6.72\times 10^6m$
