What is the molar mass of helium in kg/mol?

$4 \cdot g \cdot m o {l}^{-} 1$
But you wanted $k g \cdot m o {l}^{-} 1$.
So the molar mass of helium is $4 \cdot \cancel{g} \cdot m o {l}^{-} 1 \times {10}^{-} 3 \cdot k g \cdot \cancel{{g}^{-} 1}$ $=$ $4 \times {10}^{-} 3 \cdot k g \cdot m o {l}^{-} 1$