Part A:
The table is shown in the first picture below
From the tables, we can read that the solution

is located between 0 and 2 seconds.
The reason is that in between the interval of 0 and 2,

is turning (the cannon ball is moving toward the ground) whereas the function

increase its height. At one point these two paths will cross, as shown in the graph in the second picture below
Part B:
In the context of the problem, the one point where

and

crosses is the point where the two cannon balls will collide.