Phil tried to find the derivative of $4x+5$ using basic differentiation rules. Here is his work:
$\begin{align}
&&&\phantom{=}\dfrac{d}{dx}(4x+5)
\\\\
\text{Step 1}
&&&=\dfrac{d}{dx}(4x)+\dfrac{d}{dx}(5)
\\\\
\text{Step 2}
&&&=\dfrac{d}{dx}(4x)+0
\\\\
\text{Step 3}
&&&=\dfrac{d}{dx}(4)\dfrac{d}{dx}(x)
\\\\
\text{Step 4}
&&&=0\cdot 1
\\\\
\text{Step 5}
&&&=0
\end{align}$
**At which step did Phil make a mistake, if at all?**
[[☃ radio 1]]