Answer:
T=5.9235 seconds
Explanation:

The time it takes for the cannonball to strike the ground is the point at which H(T)=0


This is a quadratic equation and since we have a bunch of decimals we use the quadratic formula:

a=-4,9, b=27.52, c=8.9

It takes 5.9235 seconds for the cannonball to strike the ground.