If $y=ax^n$,

$\frac{dy}{dx}=anx^{n-1}$ for all rational $n$.

We'll take the following term as an example:

$\frac{3}{8}x^2$

All we have to do to terms where $x$ is to a power of anything is times the coefficient of $x$ by the original power, and then take one away from the original power.

If you are not familiar with this kind of work, these instructions may sound confusing, but it is much easier once you have seen it in practice.

We take

$\frac{3}{8}x^2$

and times $\frac{3}{8}$ by $2$, to get

$(\frac{3}{8}\times2)x^2=\frac{6}{8}x^2=\frac{3}{4}x^2$.

We then subtract one from the original power, $2$.

This gives us the final answer of

$\frac{3}{4}x^1=\frac{3}{4}x$.

Remember, don't be confused if there is no coefficient. The fact the term is there means the coefficient must be $1$, but we don't tend to write it out as, for example $1x$, we just say $x$.