Answer
$2400^{\circ}C$
Work Step by Step
The rms speed is given by equation 13–9. We see that the rms speed is proportional to the square root of the absolute temperature.
The mass stays the same, so to triple the rms speed we multiply the absolute temperature by a factor of 9.
$$T_{new}=9T_{old}=9(273+20)K=2637K\approx2400^{\circ}C$$