A mortar shell needs to be dropped into a bunker at an angle of 80 degree from level ground. The bunker is 100 yards away. How much velocity must the shell leave the cannon to accomplish this task?

If same height at both ends, symmetric parabolic path.

Goes 100 yards? I guess I use obsolete units, 300 feet and g = 32 ft/s^2

Vi = V sin 80 = .984 V
u = V cos 80 = .174 V

300 feet = u t
300 = .174 V t

how long does it take?
h = Vi t - 16 t^2
h = 0 at start and finish
16 t^2 -Vi t = 0
t (16 t-Vi) = 0
t at target = Vi/16

Vi = .984 V
so t = .0615 V
and
300 = .174 V (.0615 V)
V^2 = 28034
V = 167 feet/second