[ทิดมี สึกใหม่]

In the first diagram, the ratio of the areas of the shaded triangle and one of the unshaded triangle is (5－3):3
so that $S_A$ is one quarter of the area of the whole triangle.

In the second diagram, the ratio of the areas of the shaded triangle and one of the unshaded triangle is (5－4):4
so that $S_B$ is one ninth of the area of the whole triangle.

Now 1/4+1/9=13/36.
Hence the area of the whole triangle is (36/13)39=108 square centimetres.