Aprojectile is thrown upward from the ground at 420 ft/sec. develop the position function using the definition above. at what time is the projectile the farthest from the ground?

Given,
initial velocity () = 420 ft/s

We know,
final velocity () = 0 ft/s

acceleraction (a) = g = -9.8 m/s²
                                  =  -32.152231 ft/s²

time (t) = ?

Now, 
we know,


Now, lets find time taken to reach the height,



∴ The porjectile is farthest form the ground at t = 13.06 seconds.
∴ The highest it goes is 2743.20 feet.