A ball is thrown vertically downward with a velocity of $20\text{m/s}$ from the top of a tower. It hits the ground after some time with a velocity of $80\text{m/s}$. The height of the tower is: ($g=10{\text{m/s}}^2$)

1. A
   $360\text{m}$
2. B
   $340\text{m}$
3. C
   $320\text{m}$
4. D
   $300\text{m}$