Answer
360 m/s.
Work Step by Step
The rms speed, equation 13–9 is:
$$v_{rms}=\sqrt{\frac{3kT}{m}} $$
From the ideal gas law, PV=nRT, we see that T=PV/nR.
$$v_{rms}=\sqrt{\frac{3k}{m}\frac{PV}{nR}} $$
$$v_{rms}=\sqrt{\frac{3(1.38\times 10^{-23}J/K)}{(28)(1.66\times10^{-27}kg)}\frac{(2.9atm)(1.013\times10^5Pa/atm)(8.5m^3)}{(2100mol)(8.314J/(mol\cdot K))}} $$
$$v_{rms}=360 m/s $$