If $\overrightarrow a$ and $\overrightarrow b$ are such that $|\overrightarrow a+\overrightarrow b|=\sqrt {29}$ and $\overrightarrow a\times (2\hat i+3\hat j+4\hat k)=(2\hat i+3\hat j+4\hat k) \times \overrightarrow b$, then the possible value of $(\overrightarrow a+\overrightarrow b).(-7\hat i+2\hat j+3\hat k)=?$
$\begin{array}{1 1} 0 \\ 3 \\ 4 \\ 8 \end{array}$