Lex x represent the length of the shadow of the tree. Since the time is the same, the lengths of the shadows formed are proportional. Given that a six foot tall man cast a 5 foot shadow, for a 9 foot tall tree, the equation would be
5/6 = x/9
By crossmultiplying, we have
6 * x = 5 * 9
6x = 45
x = 45/6
x = 7.5
The length of the shadow cast by the tree is 7.5 feet