$$2Li+2H_2O\rightarrow2LiOH+H_2\\\frac{n(Li)}{n(H_2)}=\frac{2}{1}\Rightarrow n(Li)=2n(H_2)\Rightarrow \frac{1}{2}n(Li)=n(H_2)\\n(Li)=\frac{m(Li)}{M(Li)}=\frac{3g}{6,941\frac{g}{mol}}\approx0,432mol\\n(H_2)=\frac{1}{2}\cdot0,432mol=0,216mol\\V_m=24,464\frac{L}{mol}\\V_m=\frac{V}{n}\Rightarrow V=V_m\cdot n=24,464\frac{L}{mol}\cdot0,216mol\approx5,284L$$