Did he mean, "It will pass her in how many seconds"? Anyway, the watermelon will pass her in exactly the same amount of time it took this stupid teacher to come up with that question.
b. When will the watermelon hit ground?
On Tuesday.
Next question
Actually, it's a trick question. How many seconds will elapse between the time the watermelon starts passing in front of her (at head-top height) and it passes below her (at the 300 feet mark). One must know her exact height in order to come to the proper answer, as well as take in the effects of rotational jitter on her aim in tossing the fruit.