Question 12
In quadrilateral $ABCD$, $\angle BAD = \angle BCD = 90^{\circ}$. Points $E$ and $F$ are on sides $AD$ and $BC$ respectively and $AB = 5\,cm$, $CD = 10\,cm$, $DE = 8\,cm$, $BF = 6\,cm$, as shown in the figure below. If the area of triangle $BEF$ is $4\,cm^2$ less than the area of triangle $DEF$. What is the area, in $cm^2$, of triangle $DEF$?
