A balloon is filled with 3.8 L of helium gas at STP. Approximately how many moles of helium are contained in the balloon?

Approx. $0.17$ $m o l$
The molar volume of an ideal gas at $\text{STP}$ is $22.4$ $L$. We have a volume of $3.8 \cdot L$ helium gas under these conditions.
Assuming, quite reasonably, that helium behaves ideally, the molar quantity of helium gas is simply the quotient, $\frac{3.8 \cdot L}{22.4 \cdot L \cdot m o {l}^{-} 1}$ $=$ ?? $\text{moles}$ ?