A ball is thrown upwards from the top of a building of height h. The height of the ball after 75 seconds is given by 1 2 Y(t) =h+sti 5915 where h, s and g are positive constants. a) Assuming the ball is still in flight after 1 second, find the average velocity over the time interval 0 S t S 1. (Hint. Your answer may include some or all of the constants h, s and g.) b) Using the definition of the derivative, nd the instantaneous velocity at t : 1. (Hint. Your answer may include some or all of the constants h, s and g.)