Answer
$CO_2: v_{rms} = 408 \space m/s$
$He: v_{rms} = 1.35 \times 10^3 \space m/s$
Work Step by Step
$$v_{rms} = \Bigg( \frac{3RT}{M} \Bigg)^{1/2}$$ $$R = 8.3145 \space JK^{-1}mol^{-1}$$ $$20^o \space C = (20 + 273)K = 293 \space K$$
$CO_2$:
$M = 1*12.0 + 2*16.0 = 44.0 \space g/mol = 0.0440 \space kg/mol$
$$v_{rms} = \Bigg( \frac{3(8.3145 \space JK^{-1}mol^{-1})(293 \space K)}{0.0440 \space kg/mol} \Bigg)^{1/2}$$ $$v_{rms} = 408 \space m/s$$
$He$:
$M = 4.00 \space g/mol = 0.00400 \space kg/mol$
$$v_{rms} = \Bigg( \frac{3(8.3145 \space JK^{-1}mol^{-1})(293 \space K)}{0.00400 \space kg/mol} \Bigg)^{1/2}$$ $$v_{rms} = 1.35 \times 10^3 \space m/s$$
