Properties of Solids and Liquids: JEE Main 2014 Physics question

An open glass tube is immersed in mercury in such a way that a length of $8$ $cm$ extends above the mercury level. The open end of the tube is then closed and scaled and the tube is raised vertically up by additional $46$ $cm$. What will be length of the air column above mercury in the tube now? (Atmospheric pressure $=76$ $cm$ of $Hg$)