Answer: The answer would be 8.
Step-by-step explanation: I'm going to assume you mean 7 8/13 is a mixed fraction. So you multiply the denominator, 13, multiply 7 to that, then add 8 to it and the denominator would be the same as before. That should give you 99/13. When you divide, you get around 7.6, rounding closest to 8.
You would have to find the proportionality of the two. If his shadow is 3 feet long, and the tree's shadow is 9 that means it is proportioned by 3. So the height of the tree would be 15.
9 decimeters. deci = 0.1
9 *0.1 meters.
0.9 meters
9 decimeters = 0.9 meters.