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