Hi Kathy,

For 6.26, remember the bracket notation denotes area. Therefore $[ABCDEF]$ denotes the area of hexagon $ABCDEF$.

For 6.29, I'll give the following hint/example:  Suppose we wanted to show the points $A$, $B$, and $C$ were all on the same line (with $B$ in the middle). One way to show this would be to calculate the angle $\angle ABC$ and show that the angle was $180^\circ$.

Hope this helps!