Explanation:
so, the function is
h(t) = -16t² + 30t + 6
we get the point of the extreme value(s) by finding the zero solution(s) of the first derivative of the function.
h'(t) = -32t + 30
finding the zero solution
-32t + 30 = 0
30 = 32t
t = 30/32 = 15/16 seconds
after 15/16 seconds (not even a full second) the ball reaches its maximum height.
the height at that maximum is then h(15/16) :
-16(15/16)² + 30×15/16 + 6 = - 15²/16 + 450/16 + 6 =
= -225/16 + 450/16 + 96/16 = 225/16 + 96/16 = 321/16 =
= 20.0625 ft
and so, the range (the interval or set of all valid functional values) is
0 <= h(t) <= 20.0625
as naturally, on a normal surface and environment, the height of the ball cannot go below 0 (when it hits the ground, it's over).