Answer: 16 units.
Explanation:
To find the vertex, first simplify the quadratic equation into its standard form:
![h(x)=-(x+1)(x-7)\\h(x)=(-x-1)(x-7)\\h(x)=-x^2+6x+7\\](https://img.qammunity.org/2021/formulas/mathematics/high-school/lfj4udke4w2n6tq3pttde2jp7ed51b1yk4.png)
Using this formula, we can then find the axis of symmetry by using the formula S = -b/2a:
![S=(-6)/(-2)](https://img.qammunity.org/2021/formulas/mathematics/high-school/ygnjjg215ehjorya9dwz4ut98gx6fop77y.png)
The axis of symmetry lies on x = 3.
You can then substitute x for 3 in the equation to find the vertex of the parabola:
![h(3)=-9+18+7\\h(3)=16](https://img.qammunity.org/2021/formulas/mathematics/high-school/3kab2dbcyee40dme6rkbxnwuzj366jo1ki.png)
The ball will be 16 units high after travelling 3 units horizontally. This is the maximum height the ball will reach before falling.