math

an object is thrown upward from the top of a 80-foot building with a initial velocity of 65 feet per second. The height h of the object after t seconds is given by the equation h=-16t2+64t+80. when will the object hit the ground

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  1. Your equation does not match your data

    if the equation is
    h = -16t^2 + 64t + 80 , then the initial velocity was 64 ft/sec, not 65 like you typed.
    I will go with the 64

    -16t^2 + 64t + 80 = 0
    divide each term by -16
    t^2 - 4t - 5 = 0
    (t+1)(t-5) = 0
    t = 5 or -1 , we will reject the last answer

    the object will hit the ground after 5 seconds

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