Moles Questions

An oxygen cylinder of volume $30\text{litre}$ has $18.20\text{moles}$ of oxygen. After some oxygen is withdrawn from the cylinder, its gauge pressure drops to $11\text{atmospheric pressure}$ at temperature $27^{\circ }\text{C}$. The mass of the oxygen withdrawn from the cylinder is nearly equal to:[Given, $R=\frac{100}{12}{\text{J mol}}^{-1}{\text{K}}^{-1}$, molecular mass of ${\text{O}}_2=32$, $1\text{atm pressure}=1.01\times 10^5{\text{N/m}}^2$ ]