SEAMO 2027 - Paper C - SET 10 - Self-study Question 9

In trapezium $ABCD$, $AB=6$ cm, $CD=4$ cm and $AB\parallel CD$. Diagonals $AC$ and $BD$ meet at $O$. Given that $ABCD$ has area $25\text{ cm}^2$, find the area of triangle $OBC$, in $\text{cm}^2$.