Given a canon that fires rounds with a speed of 1000 m/s. There is no friction or earth curvature. The canon fires a round at some Angle1 tpwards a target. After reloading, it fires again with an adjusted Angle2 such, that both rounds impact the target simultaneaously
First, trial and error. Try to figure out at what angles the canon should fire given a specific value for reloading and aiming delay. Use the sliders to set different angles and reloading delays.
Then invoke mathematics.
Ask yourself questions like
"Given the angle of the first round and the reload time, at what angle need round 2 to be fired in order both projectile hit the ground simultaneously?"
and try to figure out how to solve them.

This geogebra applet had 3 build-in calculations.
1. Calculate AngleShot2 (given AngleShot1 and DelayShot2) so both projectiles hit the ground at the same time.
2. Calculate both AngleShot1 and AngleShot2 given DelayShot2.
3. Calculate maximum range of the canon, given som reload time.
Note: program can be instable. If erronous, reset initial values.