G1.1 Given that there are three points on the coordinate plane: $O(0,0), A(12,2)$ and $B(0,8)$. A reflection of $\triangle O A B$ along the straight line $y=6$ creates $\triangle P Q R$. If the overlapped area of $\triangle O A B$ and $\triangle P Q R$ is $m$ square units, find the value of $m$.
$$
P(12,0), Q(12,10), R(0,4) \text {. }
$$

Suppose $A B$ intersects $Q R$ at $M(x, 6)$.
Slope of $M R=$ slope of $Q R$
$$
\frac{6-4}{x}=\frac{10-4}{12} \Rightarrow x=4 ; M(4,6)
$$

Area of the overlap $\triangle B M R=\frac{1}{2} \cdot(8-4) \times 4=8 ; m=8$