If an object is thrown straight up into the air from height H feet at time 0 with initial velocity V feet per second, then at time t seconds the height of the object is :

-16.1t² + Vt + H

feet. This formula uses only gravitational force, ignoring air friction. It is valid only until the object hits the ground or some other object. Find a function F such that F(y) is the initial velocity in feet per second needed to make the maximum height of the ball be y feet when thrown from a height of 9 feet. (Enter the exact answer.)