Part (a)
The time taken by the shell to strike on the ground can be given as,
Plug in the known values,
Therefore, the time after which the shell strikes on the ground is 80 s.
Part (b)
The horizontal distance covered by the shell is,
The horizontal speed of the shell is,
Therefore, the distance covered becomes,
Substituting values,
Therefore, the horizontal distance covered by the shell is 24080 m.