Question

During World War I, the Germans had a gun

Answer 1

Before all let's just convert Km/s into m/s :
             
2.41 km/s = 2410m/s\

To solve the second part
     
First we have to find Vy Vy = 2410 m/s * sin 61.5 = 2410 m/s * 0.8788 =2117.908 m/s.
       
When the shell reaches it's maximum height the vertical velocity component will be zero
 
based on that theorem let's apply linear motion equation
                           
V = u + at
                           
0 = 2117.908 m/s - 9.8 m/S^2 * (t)
                         
t = 216.1130 s
 
As the shell has to go upward and comes back to earth the shell will require a same amount of time in order to reach earth again so the total time that shell will spend on the air will be
                     
2*t = 432.226 s 


I hope my answer has come to your help. Have a nice day ahead and may God bless you always!