IMSO 2014 — Math Division — Essay Question 5

Let $ABCD$ be a rectangle such that $AB=25$ cm and $BC=30$ cm. If $M$ is a point on $AD$ such that $\frac{AM}{AD}=\frac13$ and $N$ is a point on diagonal $AC$ such that $\frac{AN}{AC}=\frac35$, what is the area, in cm², of triangle $BMN$?