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Nvm, poor calculation on my part. Great website, thanks for taking the time to put this up.

How did you isolate T? I have been out of college algebra for awhile and have forgotten the quadratic equation.

Hi maxie.combs, thanks for the question.
$t = \dfrac{-12 \pm \sqrt{12^2 - 4 \times (-4.9) \times 70}}{2 \times (-4.9)}$
and for review
$x = \dfrac{-b \pm \sqrt{b^2 - 4ac}}{2a}$ given $ax^2 + bx + c = 0$

Make sure you look at this on Giancoli Answers since in your email it will be LaTeX gobblygook.

Hope this helps,
Mr. Dychko

For b), shouldn't the answer be negative as the direction of the velocity is downwards? Thank you.

Hi elizabeth, since the question is asking for speed, the answer will always be positive since speed is the magnitude of the velocity. Put in other words, speed doesn't care about direction, it's always a positive number.

Best wishes,
Mr. Dychko