You have two similar triangles.
Use corresponding parts of the two triangles.
If two triangles are similar, then the lengths of corresponding parts are proportional.
The small triangle has a vertical side that measures 6 ft. That side corresponds to the height of the tree, h, in the large triangle.
The small triangle has a horizontal side that measures 10 ft. That side corresponds to the side of the large triangle that measures 40 ft.
6 ft corresponds to h
10 ft corresponds to 40 ft
[tex] \dfrac{6}{h} = \dfrac{10}{40} [/tex]
