The volume of a cylindrical tank of height [tex] h [/tex] and radius [tex] r [/tex] is
[tex] V=\pi r^2h [/tex]. Here [tex] h=1.2\;,2r=4.6\;m,r=2.3\;m [/tex].
Substituting numerical values,
[tex] V=\pi (2.3)^2(1.2)=19.943\;m^3 [/tex]. When the tank is half full, the amount of water the container holds is
[tex] \frac{V}{2}=19.943/2=9.971\;m^3 [/tex]