VTMO 2026 - Grade 5 - Final - SET 2 - Self-study Question 5

In rectangle $ABCD$, take $M$ on $AB$ and $O$ on $MC$ so that $MO:OC=1:3$. Line $DO$ meets $AB$ at $N$. The two shaded triangles have total area $10\ \mathrm{cm}^2$. Find the area of rectangle $ABCD$, in $\mathrm{cm}^2$, and explain.