 change
      in $y$ called $dy$)? What is the run (i.e, the change in $x$
      called $dx$)?</li>

      <li>We already know the slope of the tangent line is the
      derivative $f'(3)=6$. We also know the slope from the
      previous part. These two must be equal. Use this fact to give
      an equation of the tangent line to $f(x)$ at $x=3$.</li>
    </ol>
  </div>

  <div class="problem" id="diff-sphere">
    <div class="marginpar bmw">See 3.11:45-62.</div>
    The manufacturer of a spherical
    sto