JEE Math Practice Question

In a triangle $P Q R$, let $\vec{a}=\overrightarrow{Q R}, \vec{b}=\overrightarrow{R P}$ and $\vec{c}=\overrightarrow{P Q}$. If \[ |\vec{a}|=3, \quad|\vec{b}|=4 \quad \text { and } \quad \frac{\vec{a} \cdot(\vec{c}-\vec{b})}{\vec{c} \cdot(\vec{a}-\vec{b})}=\frac{|\vec{a}|}{|\vec{a}|+|\vec{b}|}, \] then what is the value of $|\vec{a} \times \vec{b}|^{2}$?