Question 1167023
.
<pre>

Regarding this problem, notice that both these formulas describe the projection of the position to the vertical direction.


They do not describe a trajectory of the ball, which is usually a parabola in (x,y)-plane.


In football, it is a rare case, when the ball moves vertically up --- so the question and the problem itself are not very realistic.


If, nevertheless, these circumstances do not embarrass you,  then consider this equation


    -4.9*𝑡^2 + 18𝑡 + 0.8 = -1.43t + 4.26


and solve it for t.


Solving this equation is a mechanical work, so I leave it to you.
</pre>

--------------


In my personal view, the posed problem is not adequate to reality.