Helium, M = 4.003 g/mol, and nitrogen, M = 28.02 g/mol, are at 400 K…

Step 1. Helium. $u_{\text{rms}} = \sqrt{\dfrac{3 \times 8.314 \times 400}{4.003 \times 10^{-3}}} = 1579\ \text{m/s}$.

Step 2. Nitrogen. $u_{\text{rms}} = \sqrt{\dfrac{3 \times 8.314 \times 400}{28.02 \times 10^{-3}}} = 597\ \text{m/s}$.

Step 3. The ratio. $\dfrac{1579}{597} = 2.65$. It also equals $\sqrt{\dfrac{28.02}{4.003}} = 2.65$, as the formula says.

Step 4. The kinetic energy. $\tfrac{3}{2}RT = 1.5 \times 8.314 \times 400 = 4988\ \text{J/mol} = 4.99\ \text{kJ/mol}$. It is the same for both gases.