In the Cartesian coordinate plane; a triangle with one vertex at the origin and the other vertices on the lines $y = x$ and $y = - x$ has its medians intersecting at point $(2,4)$.
Accordingly, what is the area of this triangle in square units?
A) 18
B) 24
C) 27
D) $9 \sqrt { 2 }$
E) $18 \sqrt { 2 }$