Using the product rule, we have
so that
The equation of the tangent line to <em>W(x)</em> at <em>x</em> = 7 has all the information we need to determine <em>m'</em> (7).
When <em>x</em> = 7, the tangent line intersects with the graph of <em>W(x)</em>, and
<em>y</em> = 4.5 + 2 (7 - 7) ==> <em>y</em> = 4.5
means that this intersection occurs at the point (7, 4.5), and this in turn means <em>W</em> (7) = 4.5.
The slope of this tangent line is 2, so <em>W'</em> (7) = 2.
Then