Question 270253
The height in feet of the baseball above the ground is given by h(t)= -16t^2+55t, where t represents the time in seconds after the ball is thrown. How long is the ball in the air? 
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h is the height of the ball.  Since it's thrown and caught at apx the same level above ground, that is the zero level.
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Find when the height = zero.
0 = -16t^2 + 55t
t = 0 and t = 55/16
t = 0 when it's tossed, and t = 55/16 seconds when it's back to the same level, so its flight time is 55/16 seconds.