MathNet 2018-part-04 — 181 problems (EN–VI) Question 28

In $\triangle ABC$, the length of $AB$ is $12$ and its incircle $O$ has radius $4$. Let $D$ be the point of tangency of circle $O$ with $AB$. If $AD : AB = 1 : 3$, find the area of $\triangle ABC$.