In a closed organ pipe, the frequency of fundamental note is $30 \mathrm{~Hz}$. A certain amount of water is now poured in the organ pipe so that the fundamental frequency is increased to $110 \mathrm{~Hz}$. If the organ pipe has a cross-sectional area of $2 \mathrm{~cm}^2$, the amount of water poured in the organ tube is $\underline{\hspace{2cm}}$ g. (Take speed of sound in air is $330 \mathrm{~m} / \mathrm{s}$)