A ball is thrown vertically upwards with a velocity of $19.6 \mathrm{~ms}^{-1}$ from the top of a tower. The ball strikes the ground after $6 \mathrm{~s}$. The height from the ground up to which the ball can rise will be $\left(\frac{k}{5}\right) \mathrm{m}$. The value of $\mathrm{k}$ is __________. (use $\mathrm{g}=9.8 \mathrm{~m} / \mathrm{s}^{2}$)