This problem concerns projectile motion. A cannon shoots a projectile at an angle, yet the ground is not flat, but slants downwards, which essentially lets the projectile fly longer. Here we solve both for the (horizontal) range of the projectile, and the best angle to fire the cannon to achieve maximum range.
This problem is a little intensive on the mathematical side, and is one of our longer solution videos.
Solution by Yaşar Safkan
You will find that the algebra and trigonometry is a bit tricky towards the end.