The height of the kangaroo is 4 feet and it's shadow is 9 feet. The relationship between the kangaroo and its shadow is 4/9. This has to be equal to that of the eucalyptus tree. The relationship of the eucalyptus tree is x/36.
4/9=x/36
You can either solve for x by realizing that in order to get from 9 to 36, you multiply by 4 and therefore have to multiply 4 by 4 to get x.
Or you can solve for x by cross multiplication. 36(4)=144. You then divide 144 by 9.
Either way, x = 16 and the height of the tree is 16 feet.