Joan Is Looking Straight Out a Window of an Apartment

question 80

Short Answer

Joan is looking straight out a window of an apartment building at a height of 20 ft from the ground. A boy throws a tennis ball straight up by the side of the building where the window is located. Suppose the height of the ball (measured in feet) from the ground at time t is
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At what time(s) does the ball cross Joan's line of sight?

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