This is a quadratic equation, so we can solve for all of this with a graph!
sorry i cant include an image but you can graph it yourself on desmos or some other calculator
the initial height is 7 (we see this from the equation, the c therm is the y intercept (initial height))
the cannonball will hit the ground at the positive x intercept, which is (2.1,0)
the maximum height is (0.9,21.1)
hope this helps!