How is this equation completed? i cannot find any examples in the book.

Option D

Step-by-step explanation:

Note that the projectile height as a function of time is given by the quadratic equation

To find the maximum height of the projectile we must find the maximum value of the quadratic function.

By definition the maximum value of a quadratic equation of the form

is located on the vertex of the parabola:

Where

In this case the equation is:

Then

So: