$\mathscr{E} = \dfrac{1-2x}{2x+1} + \dfrac{x^2 + 3x}{4x^2 -1} \div \dfrac{3+x}{4x+2}$

Let $x = 2016$. If $\mathscr{E}$ can be represented in the form $\dfrac{a}{b}$, where $a$ and $b$ are coprime positive integers, find $a+b$.

You may use a calculator for the last step.