[tex]\displaystyle m=4~kg;~\Delta l=10~cm\\ \\ G=mg\Rightarrow G=4 \cdot 10 \Rightarrow \mathbf{G=40~N}\\ \\ F_e=k\Delta l \Rightarrow k=\frac{F_e}{\Delta l} \\ \\ \Delta l=10~cm=0,1~m\\ \\ F_e=G=40~N\\ \\ k=\frac{40}{0,1} \Rightarrow \mathbf{k=400~\frac{N}{m}}[/tex]
