there are two main ways to go about this. we can complete the square to get the function in the form: , in which gives the vertex
or we can use the vertex formula: , where b is the coefficient of d and a is the coefficient of d^2
do whichever you are comfortable with.
at the moment the player releases the ball, the horizontal distance from the player to the ball is zero. just plug in d = 0 and solve for hc) How far fromt he ground is the ball when the player releases it?