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I have posted a link there to this topic so the OP can see my work.Average Velocity and instantaneous velocity?

I am having so much trouble with this question, and I have no idea why. I know that average velocity is based upon a secant and is basically a slope formula. Instantaneous velocity is based upon a tangent and is basically a point. However, this question is confusing me, maybe I'm staying up too late. Help?

When a ball is thrown vertically upward into the air with a velocity of 72 ft/sec its height, y(t), in feet after t seconds is given by y(t) = 72t - 16t^2. Find the average velocity of the ball over the interval from 4 to 4+h seconds, h does not = 0.

a) Avg. Vel.= -(57-16h) ft/sec

b)Avg. Vel.= -(57+h) ft/sec

c) Avg. Vel.= -(57+16h) ft/sec

d) Avg. Vel.= -(57-h) ft/sec

e) Avg. Vel.= -(56+16h) ft/sec

f) Avg. Vel.= -(56-16h) ft/sec

Then it proceeds to ask:

Find the instantaneous velocity of the ball after 4 seconds:

a) Instantaneous Vel. =-56 ft/sec

b) Instantaneous Vel. =-55 ft/sec

c) Instantaneous Vel. =-53 ft/sec

d) Instantaneous Vel. =-54 ft/sec

e) Instantaneous Vel. =-57 ft/sec